How Much Exactly Is 2.0 mg/cm^2—The Amount of Sunscreen Necessary to Achieve the Labeled SPF Rating?

Personal/Inspirational, Skin Care

****This post is authored by John Su.

In many, MANY posts that I have authored, the number 2.0 mg/cm2 —the amount of sunscreen necessary to achieve the labeled SPF rating, has been thrown around more times than I can count. Naturally, people ask, “How much is that exactly?” Well, today’s your lucky day!

First, we need to convert 2.0 mg/cm2 into units that we can understand, namely ounces and inches. (Keep in mind that I’m will not be obeying significant figures or rounding rules)

  2.0 mg              (2.54 cm)2        (12.0 in)2           1.0 g            1.0 oz        ~0.0655 oz

————–    X    ———–     X    ———-    X    ———-    X   ———   =   ————–

1.0 cm2            (1.0 in)2           (1.0 ft)2         1000 mg        28.35 g            1.0 ft2

As you can see 2.0 mg/cm2 comes out to ~0.0655 oz/1 ft2.

Now, assuming that you have a facial sunscreen, and a separate one that you use on the rest of the body including the neck and ears (which I do), we need to know how the total surface area of your face.

I know you hate math, but don't you dare pull this $@#% on me!
I know you hate math, but don’t you dare pull this $@#% with me!

The average human face is ~0.60 ft2. In order to calculate this amount:

  1. Find a measuring tape or a flexible ruler.
  2. Take the end of your tool and place it on the front of your left ear, without blocking the opening.
  3. Holding the tool as close to your face as possible, drag it across your face until it reaches the opening of the right ear.
  4. Record that length (X).
  5. Then again, take the end of your tool and place it at the edge of your hairline directly above your nose.
  6. Holding the tool as close to your face as possible, drag it across your face until it reaches the chin.
  7. Record that length (Y).
  8. Finally, you can add an inch to either lengths if you want to factor in how prominent your features are.

So for me, my X = 12 inches, and my Y = 8 inches. Considering that my face is widest at the measuring point for X, which means that measurement was an overestimation; and that my face isn’t very flat, which means that my Y measurement was an underestimation; means that I don’t have to adjust my numbers because the two characteristics effectively cancel each other out.

Therefore, my facial sunscreen needs to cover 12.0 in X 8.0 in = 96 in2. To convert from in2 to ft2, we need to do the following:

96.0 in2          1 ft2           ~0.667 ft2

———    X   ——–     =   ————

1.0             (12 in)2             1.0

As you can see, my sunscreen needs to cover ~0.667 (or two-thirds) ft2.

Therefore, to find out how many ounces of facial sunscreen to use, I need to multiple that amount with ~0.0655 oz/1 ft2.

   0.667 ft2        0.0655 oz     ~0.0437 oz

———–    X   ———–   =   ————-

1.0               1.0 ft2               1.0

The math comes out to be ~0.0437 oz. To a bit more accurate, let’s convert that into mL.

0.0437 oz      28.35 g        1.0 mL       ~1.2439 mL

————   X  ———   X   ——–   =    ————-

1.0            1.0 oz           1.0 g               1.0

Because 1 g = ~1 mL, that comes out to ~1.2439 mL. This works perfectly for my example.

The sample size is 1.15 mL.
The sample size is 1.15 mL.

Yesterday, I received a sample of a moisturizer (pictured above) from my Sephora Chic Week order that contained slightly less than that amount (1.15 mL).


So I proceeded to empty the entire sample into the palm of my hand (pictured left). Then, I put an approximately equal amount of sunscreen in my other palm (pictured right).

THAT’S how much sunscreen I need (and what most people need) for the face alone, though I admit that my face is a bit larger than normal! I know, it’s a lot, but tough! MAKE IT WORK! Haha. One of the readers (Sarah) suggested to apply half that amount of sunscreen in two layers, meaning that you apply 1.0 mg/cm2 to your face, wait for it to dry, and then apply the second 1.0 mg/cm2 layer of sunscreen! It’s a good idea that may allow for a more cosmetically acceptable finish. Give it a try.

Also, I would recommend getting a sample that contains about how much sunscreen you should be using per day (around 0.04 oz), and do what I did with these two pictures. Remember how much sunscreen you used in your version of this experiment. That way, YOU will actually know about how much you need to apply on a regular basis. You can then use that amount to gauge and compare how much you actually use, and try your best to work up to that amount!

Also, if it’s available to you, consider buying a separate 1/4 teaspoon to measure your daily facial application amount of sunscreen. 1/4 teaspoon is approximately the amount that most people need to apply to achieve 2.0 mg/cm2. Let’s see how my face’s surface area matches up to this claim.

  0.0437 oz        6.0 tsp       ~0.2622 tsp

  ————   X    ———–    =    ————–

1.0               1.0 oz               1.0

Yep, that’s about one quarter (1/4 = .25) of a teaspoon! So yeah, consider buying a separate 1/4 teaspoon from any grocery or drugstore. I’d like to thank reader (Maggie) for suggesting this!

Consider buying a separate 1/4 teaspoon for your daily facial sunscreen application amount.
Consider buying a separate 1/4 teaspoon for your daily facial sunscreen application amount.

But going back to the application amount, that’s why it’s so difficult for me to recommend more expensive sunscreens. For example, the Algenist Ultra Lightweight UV Defense Fluid SPF 50 provides great UVA and UVB protection with 17.1% zinc oxide, 2% titanium dioxide, and 7.5% octinoxate. But at $38.00 for 1.0 oz, it’d be used up really quickly.

How quickly? Well for me, assuming that I apply it once per day, here’s the math:

        1.0 oz         1.0 day        ~22.88 days

     ————  X  —————–  =  —————–

   1.0             0.0437 oz             1.0

That’s about three weeks! There are 356.24 days in a year, which means that on facial sunscreen alone, I’d be spending over $600 per year! That’s insane! Okay, I can bring that number down a bit by considering the fact that I’m not outside every day, and that there are sales throughout the year. Plus, I could stock up during these sales. But still, I’d estimate the final number to be well over $500.

But to each his own, right? I can’t see myself spending that much on sunscreen, but eh. *Shrugs* Anyways, I hope this was an enlightening post on what exactly 2.0 mg/cm2 means.

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  • L

    Please tell me if the 1/4 tsp. rule applies to all zinc sunblocks.

    Also, does the 1/4 tsp. rule apply to face only, or face, ears & neck?

  • @Alejandra

    I know, right?! I don’t know if you saw, but I did a follow-up post on my blog about the 1/4 teaspoon rule. I commented that mine looks ridiculously small! However, once you fill it up to the top, it’s actually quite a lot of sunscreen. You’ll probably want to let it set for 5-10 minutes, just so it doesn’t move when you apply something over it. Of course, you can consider using something that’s tinted, so you can skip foundation and just use a bit of concealer and powder. Of course, you can mix in a foundation/bb/cc/cream that contains inorganic UV filters as well to achieve coverage.

    As for using sunscreens that only contain 20-22% of (coated) ZnO, you can certainly use them on a daily basis as your sole source of sun protection, assuming that you’re not in the sun a lot on a regular basis. The main weakness of ZnO is that it doesn’t provide a lot of SPF protection–it hardly reaches over SPF 15 at 25%. (Of course, the vehicle can affect the efficacy of ZnO.) But those are stuff that you can’t quantify by just looking at the ingredients list. (More on this topic when I publish the Sun Protection page on the blog–mid-September) So if you’re not really in the sun very long, and/or not in the sun during the hottest parts of the day (~10 am-4 pm), when UVB rays are the strongest, you should be fine using those types of sunscreens. But when going to the beach, you’ll want a stronger sunscreen. Or you can layer it over another equally good sunscreen. Or… just apply more than 2.0 mg/cm^2. Lol!

    And it’s sort of ironic and unfortunate that you can’t easily access EltaMD, because I was going to suggest one of their other products, which provides similar levels of overall protection (actually slightly more), and is also tinted, which avoids a heavy white cast–something that I know the SPF 47 has. <<< Run-on sentence, anyone? Anyways, it's the SPF 41 from the same line. But yeah, let me know if you have any products you'd like to ask me about. 🙂

  • Alejandra

    John, I just got my 1/4 teaspoon, its a lot of sunscreen! Ill see how I get used…..I have a doubt about mineral sunscreen regarding your last comment, do you recommend a pure-zinc oxide sunscreen (20-22%) or the protection is better if its combined with titanium dioxide (10% z.o, 5% t.o for example).
    Ive been using the Elta MD UV pure spf 47 sunscreen but its hard to find for me so Ive been looking for other options for oily skin.
    Thank you.

  • @Lillian Pham

    I know, right?! Wouldn’t it be great if that were actually true? As for the inorganic vs organic thing, I actually did a series on FutureDerm discussing just that, as you stated in your response. There are 5 parts, and it’s quite a heavy read. Here’s the link for the final part, which contains a summary of everything discussed, as well as links for parts 1-4, in case you want more details:

    As for zinc oxide (ZnO) blocking all types of UVA rays, well it’s far more complicated than that. But I cover most of that in post that’s linked above. In short: ZnO may have the most “ideal” spectral profile in terms of providing uniform protection, at least out of the UV filters available in the US. But it’s so inefficient that you have to use formulations with pretty high concentrations of ZnO in order to get at least adequate protection.

  • Lillian Pham

    @ John Su

    Aww I am sad to hear this! I was using a zinc oxide and titanium dioxide sunscreen and it was making my face white if I used too much. Now I am considering chemical sunscreens if what you say is true, but first I need to figure out if using chemical or non-chemical is better. I heard non-chemical was better because something about zinc oxide being the only ingredient that actually blocks all types of UVA rays. I know there are zinc oxide and titanium dioxide sunscreens out there that don’t make your face white so now I will have to look again. Ahh so many options, but only a few that truly work! I saw earlier that you had an article of organic vs. inorganic sunscreens so I will look at that when I have time.

  • @Firn

    Good to hear. 🙂

  • @Lillian Pham

    You know, I’ve also heard this mentioned before. And surprisingly, the person I heard it from is a rather well-known dermatologist on YouTube. Unfortunately, like with anyone, mistakes or misconceptions will be made.

    Anyways, I have never seen any published data, references, etc., that suggest, infer, or even present theories to even remotely affirm the notion that you can apply comparatively less of an inorganic sunscreen, in order to achieve the same amount of protection as a correspondingly similar organic sunscreen would provide.

    And this makes sense, because EVERY single product–including lip balms, that has an SPF rating in the title and has an “Active Ingredients” section denoting the concentrations of the UV filters present (at least in the USA), is tested en vivoin vivo

  • Firn

    Dear John,

    I suspected as much. Am going to stick with my oil cleanser that does the job beautifully and gently.

  • Lillian Pham

    Does this amount apply to non-chemical sunscreens, which contain zinc oxide and titanium dioxide? I heard that with non-chemical sunscreens, you don’t have to apply as much sunscreen as a chemical sunscreen. So you can achieve the labeled SPF rating of a non-chemical sunscreen by applying less than a chemical sunscreen. I think that’s why people don’t like non-chemical sunscreens because they complain that it makes their face turn white, but I think it’s because they are applying more than they need to. Can you clarify this? Thank you!

  • @Firn

    Yep, baby oil would remove your makeup. But then there’s nothing to remove the oil and dissolved makeup. You’ll be left with a wonderful layer of grease, and would therefore have to use a rather potent detergent-based cleanser. 🙁

  • Firn

    Dear John,

    Thanks for your reply. I have been trying out an oil cleanser (oil + detergent, hurrah) and it seems to be working well. My mum (who also has very reactive skin) claims that I should be just using baby oil (scented mineral oil) to remove my sunscreen but I am worried that because it doesn’t come with any detergents to help it rinse off that I will not be removing it completely.


  • @RP

    I’m sure that you know that with your condition, the best thing to do is to avoid the sun as best as you can. Wear huge sunglasses, lots of sun protective clothing (considering investing in some that are specially designed to block UV rays), and of course, very potent sunscreens.

    Because it’s difficult to elucidate if you are more prone to UVA or UVB light, it’s best to simply use a sunscreen that is highly protective against both types. And since it appears that you have access to the Mexoryls, Tinosorbs, and the other newer UV filters, many of the recommendations that I’d give to you, will likely be not as potent since I live the US, and am a lot more familiar with what is available here. Therefore, I think it’s best if you give me a list of sunscreens that you’re interested in trying, so that we can evaluate them and proceed from there.

  • RP

    Hey John, I just ran into this article and it is very informative! Definitely learned a lot from it. I was wondering if you could provide me with any recommendations? I suffer from polymorphous light eruption so I’m not too sure if the sunscreen I purchase should be any specific kind. For the past few years as I learned more about my skin condition I’ve tried out so many different kinds of sunscreens and only one really worked out for me (ombrelle 60 SPF), but only for a year (not sure why). But my second issue is that I get acne on my face so greasy sunscreen doesn’t work too well for me. Can you direct me to your favourite sunscreens? Or maybe if you know of any that will be well suited for my situation? Thanks for your help!!

  • @Robert

    It depends on the size of the neck, but the application amount is generally about the same amount as the face. To approximate this, use a measuring tape and measure both the circumference and length of your neck. Then multiple them together to get the total surface area. Work that number into the relevant equations in the article above, and viola, you’re done.

    Same goes for the hand; it’s really not complicated! Given the various curves and irregularities of the hand, it’s probably easiest to approximate your hand as a rectangle. Hold your hand against a flat surface and take measurements of the widest and longest points of your hand. Multiple those two numbers together to get the total surface area (of your hand). Like above, work that into the relevant equations above, and you’re done! 😉

  • Robert

    Should we be using the same amount for the neck as well? And to really make things interesting, what formula tells you the precise amount to use on each hand? 🙂

  • @Emma J

    Haha, that’s fine. I assure you that the math is correct. 🙂

    But if you’d like me to walk you through the steps and answer any specific questions, let me know.

  • Emma J

    I don’t remember those particular calculations from my school days, so……….it looks like I should get back there and learn all about the mathematics of sunscreen

  • @Firn

    Course, you’re welcome!

    That’s good to hear. How do you like the LRP BB cream? Also, can you link what the FDA said about oxybenzone that’s making you worry?

    As for how to effectively remove very water-resistant sunscreens, use an appropriately strong detergent-based cleanser that also contain good amounts of some type of oil. It can be anything ranging from mineral oil to a non-fragrant plant oil such as olive oil. Gently massage the cleanser into your face in circular motions for maybe 30 seconds. This way, the oil content will help soften and loosen the “dried/set” sunscreen, and the detergents will allow the little oil and sunscreen blobs that form to mix with the water from your sink. Therefore, when you finally rinse, the water will carry everything away.

    The above-described cleanser basically does in one step, what you’re currently doing in two.

  • Firn

    Thanks for the reply, John. Yes, my foundation does have TiO2 in it plus other organic sunscreen molecules. At the moment, I am trying to find a dupe for my fabulously expensive and thick derm-prescribed sunscreen (which also has oxybenzone, which I am trying to avoid after that FDA statement on its toxicity).

    I am now using the La Roche-Posay Uvidea XL Melt-in BB cream, which has lots of stable organic sunscreens and TiO2.

    I find that I tend to have breakouts if I apply a lot of sunscreen (hot 36C and humid almost 90% humidity climate I live in). So it’s hard to choose between protection and acne. :'(

    What is the best way to cleanse my skin to effectively clean out all the sunscreen? I use Bioderma Crealine and follow with SebaMed Clear Skin bar soap because it seems to be the only combination that does it…

  • @Sarah

    Lol @ the Cerave SPF 50! You know, despite the relatively low % of UV filters, Cerave still manages to screw up their new product line. 🙁 And despite using “InVisibleZinc,” it’s the TiO2 that makes the sunscreen super white, due to its much higher refractive index. Yay for false advertisement? Haha!

    The SPF 30 is made up of primarily sunflower and jojoba oil; hence the grossness. 🙁

    As for the Clinique product, oh no! That’s such a shame, because it’s really a pretty great sunscreen on paper. But good review! I guess the search goes on for you?

    By the way, did you get that subscription issue sorted out?

  • Sarah

    John, I guess great minds do think alike! haha…because I just picked up the Clinique City Block SPF40 last week! I’ve been considering it ever since they reformulated earlier this year, and finally picked it up after being so disappointed with two others that I’ve tried. I love my CeraVe PM so much that I decided to give their new suncare line a try. But the CeraVe Sunscreen for Face SPF50 is so thick that it is borderline line a lightweight toothpaste! And the white cast is very bad, and I’m only a NC20 at the moment.

    The other one I tried by random while browsing at Whole Foods is the Andalou Naturals Oil Control Beauty Balm Un-tined with SPF30. This one is absolutely horrible! There is no oil control, in fact, it is very oily on my slightly drying skin. The white case is even worse than CeraVe’s. This one feels like straight up toothpaste! I don’t believe the tinted version will be any better either.

    Anyways, back to Clinique…I think it’s a decent product. The tint only provides very minimal coverage. The product looks like foundation color in the tube, but once spread out, it actually it’s more like a very light white-ish/primer color, and not really a beige-y color. It does not control oil throughout the day, but the product itself isn’t greasy. So far so good, right? Well, the problem I have is that this somehow balls up on me. As I’ve mentioned before, I like to apply two layers of sun protection on my face. It takes longer, but I like it better that way than to have all the 2.0 mg/cm^2 applied at once. On the first layer, it is fine, the balling up is tolerable. However, on the second layer, it balls up so much that I had to use a clean foundation brush to wipe off the residue. I can imagine that this will be even worse if I layer my actual foundation on.

    For the record, I do not use any gel type moisturizer underneath. I’m still planning to try it out for another week first before making my final decision. But for now, it is a miss for me, which is very unfortunate, because the price is so great and it’s easily accessible.

  • @Emy Shin

    I’ve always used the Cream version in the past, despite having very oily skin. Recently, I got samples of the reformulated version of both types (lotion, cream), and I have to say that the lotion is so much less white than the cream! However, I do admit that it remains rather greasy (despite being very thin in texture), that takes a long time to set. But I don’t find it particularly whitening, at least not compared to several others I’ve used. But it’s good to hear that you like the old formulation. And wow, three backups!

    As for the Elta MD sunscreens, the reason why I recommend them is because they provide acceptable to good levels of sun protection, while being very cosmetically elegant for the most part. But it’s not because they provide a lot of protection. While I would likely never use them on MY face, because I recommend products to people who have a wide range of expectations, I have to downplay my own standards because let’s face it, many people are not as particular or peculiar. 😉

    Finally, as for a good inorganic-based sunscreen, I just found this earlier last week. The Clinique City Block SPF 40 was recently reformulated with higher amounts of UV filters [Zinc Oxide (9.6%), Octinoxate (7.5%), Titanium Dioxide (7.3%), Octisalate (2%)], and a more pleasing texture. Furthermore, because it’s tinted, you don’t have to worry about a prominent white cast. You may not even have to mix in any foundation and/or apply a heavy powder foundation to give you coverage! Just dab on a bit of concealer where you need it, set everything with a translucent powder (or whatever you’d like) and you’re good to go. Based on the BASF sunscreen simulator, the Clinique SPF 40 provides almost the same amount and type of protection (UVB, UVA) as the old Shiseido SPF 60. It actually gives a higher PPD/UVA-PF rating overall, though the UV spectral profiles of the two sunscreens aren’t identical. Regardless, I’d definitely recommend picking up a sample of this. I’m so happy that they reformulated it! And the price isn’t too shabby too.

  • John, I actually tried out the newly reformulated Shiseido SPF50+ lotion a few months ago. I was excited because of the higher ZnO concentration: 19+%. Unfortunately, it didn’t work out for me. It was very similar to the SPF60 version, but noticeably more whitening. The texture was also slightly different, a bit thicker, but nothing bad. However, because of how whitening it was, I had to return it (the older version, SPF60, is as whitening as my skin tone can stand without looking like a Geisha).

    It would be good for those who has lighter skin than I do (I’m around NC25), or for those who mix sunscreen with their foundation.

    Luckily, I still have 3 bottles of the SPF60 version I bought last November during the F&F sale, which should last me until the end of the year. But I’m testing out other sunscreens (i.e. the Kanebo ALLIE one) for when these run out. 🙂

    I’ve thought of trying the Elta MD ones, since they came so highly recommended from you and others on this blog, but the UVA protection they offer (with ~9% ZnO) is a bit low for me. If you ever find a good sunscreen with high ZnO concentration but not terribly whitening, please do let me know! Buying Japanese sunscreens from overseas without any discounts can be terribly painful for my wallet. 🙂

  • @theresa

    As stated in the original response, the important thing to remember is that there is a lot of uncertainty and variability when it comes to correlating application amount and SPF values–something that the study clearly states. Many factors can influence the results. I mean, that’s what a correlation essentially is. There is no definite or exact answer.

    Ultimately, the goal is to apply 2.0 mg/cm^2.

  • @Emy Shin

    Thank you for the support!

    As for the Kanebo sunscreen, I agree that because the % of UV filters is not disclosed, there’s no way to be absolutely sure. But by drawing from the spectral profiles of the three UV filters present, how they are placed in the ingredients list, and the PA++++ rating listed, it would appear highly likely that this provides very good overall protection. But as we both said, there’s no way to be sure.

    By the way, the Shiseido lotion was recently reformulated. Maybe give it a try and let us know how you like it? 🙂

  • theresa


    It does make sense. You are saying that theoretically if one can achieve absolutely uniform application then SPF and application amount are linearly correlated. I will have to research that further and read the studies in more detail but at least I now understand the point you were making. I think sometimes it is hard to convey innuendo in writing and honestly I am not good at “reading between the lines” and guessing what someone is getting at.

    I do have a question on one of the studies. The Kim study from 2010 on Asian skin states in the Background section, “Theoretical calculations have suggested that the effectiveness of SPF is related to sunscreen quantity in an exponential way but this was not confirmed in Asian skin.” This goes along with what you stated. Yet the conclusion states, “The relation between the amount of sunscreen applied and the SPF provided was most likely to follow exponential growth.” Of course, the study does mention limitations but my understanding of the study is that the results showed that SPF and application amount are exponentially related and if one looks at the graphs for the two sunscreens tested this would support the claim for exponential relationship. Sort of confusing if you ask me. What is your take on it?


  • Thanks for all your contribution to FutureDerm! I’ve learned a lot from all of your posts, and am glad I will still be able to find them over at your blog. 🙂

    Personally, I try to use at least 1ml of sunscreen for my face each day. However, even though I am on the lighter side of medium Asian skin tone, most conventional sunscreen still whiten my face considerably when used the right amount. I’m currently using the Shiseido SPF60 sun lotion, which has ~16% ZnO; it’s tolerable, but still lightens my skin.

    I’m currently testing out some of the Japanese sunscreens, including the Kanebo Allie UV Protector sunscreen. Japanese companies don’t disclose their percentages, but considering ZnO is the second ingredient (listed by percentage), plus the fact that it’s PA++++ / PPD16+, I’m using it based on faith. So far, it still whitens my skin a little when applied the correct amount (which is something I’ve come to accept for sunscreens with decently high ZnO values), but it’s the most comestically elegant sunscreen I’ve used yet.

    P.S. Thanks to you and Maggie for the suggestion of buying a 1/4 teaspoon measure for sunscreen. That’s a brilliant idea. 🙂

  • @theresa

    Actually, if you look at the source article where Dr. Pinnell obtained that information (, you’ll see that this data was taken from sunbathers who applied the sunscreen themselves. Furthermore, you’ll also notice that the source material was published in 1997. A lot more situational and conditional observations have been made since then–most importantly, uniformity in sunscreen application. Back then, researchers simply extrapolated the data obtained from their observations to make a blanket statement that SPF values and application amount are always exponentially correlated. However, that’s only because the measurements were taken from unevenly applied sunscreen–something that is highly probably at such low amounts (0.5, 1.0, etc). Theoretically however, if a uniform film can be achieved, the SPF ratings would be more linearly correlated with the application amount, and this is supported by published data:

    As you can tell from this post published in 2003 ( uniformity and evenness can significantly influence SPF values.

    This study published in 2010 (, suggested that the previously thought notion that SPF values and application amounts are exponentially correlated, is not always true. The study indicates that the true SPF value would be difficult to predict from in vivo measurements (like from sunbathers) due to a lack of uniformity.

    This study published in Nov. 2012 ( further substantiates the previous article’s conclusion that there was a wide range of observed SPF values when it came to manipulating application amount. “It can be seen that when the dose is halved, the SPF is divided by a variable factor according to the product***, from 1.5 to 3.8.” Note that dividing by 1.5 is actually LESS than the theoretical linearly correlated tendency of dividing by 2 for half the application amount.

    Finally, this study published in Dec. 2012 ( demonstrated that using sophisticated laboratory settings, it was shown that SPF values and application amount were linearly correlated.

    As you can see, what you’re claiming is a limited truth, because it is incomplete.

    The intent of my original comment that you quoted, was to establish that theoretically (meaning when applied uniformly–something that is most likely only achievable in theoretical and laboratory settings since the average human just doesn’t have the kind of muscle control to achieve an even layer of sunscreen at that lowered density) with JUST the UV filters in a simple vehicle, application amount and SPF values are linearly correlated. Note that the BASF sunscreen simulator also supports this theory.

    But as most people can tell from the overall tone of the original comment, the main focus and message that I tried to convey was that “2.0 mg/cm^2 is required to achieve a reliably even layer.”

    Maybe I should have included the word “theoretical.” But I assumed that most people would grasp the underlying innuendo regardless. I was clearly wrong, and I apologize for that ambiguity.

    Does that all make sense?

    ***Note that another aspect that can largely affect the above-discussed relationship between SPF values and application amount, is the inclusion of antioxidants and anti-inflammatories, whose efficacy is dependent upon the amount of UV filters present to protect them, so that they can do their work. Make sure to read this post for more detail:

  • @Eileen

    Teehee. 😉 Good use of the word “brouhaha” by the way! I don’t think I’ve personally ever used that word except to describe when my best friends were talking about my first (highly-disastrous) blind date. Sigh.

    But yeah, it’s insane that you had to special order sunscreens back then. I mean wow, have times changed! And Lol @ “Use a spoonful.”

  • @Belle

    Haha, small faces are great, too! But the application amount for you is not so different than that for me. 0.1998 tsp is basically 1/5 of a teaspoon, so you can still use the 1/4 tsp rule, and just use a little less. But half of a 1/4 teaspoon is only 1/8, which is definitely not enough. Sorry, you can’t use just half the recommended amount. 🙂

    To sum that all up:
    1/4 tsp = 0.25 tsp
    1/5 tsp = 0.20 tsp

    It’s only a small difference, so you can still use the 1/4 teaspoon measuring technique.

  • @Catarina

    Yay, that’s great to hear! Go out there and buy yourself a 1/4 teaspoon! Haha.

  • theresa

    Re: your comment

    “As for applying half the amount of sunscreen, you will then get half the amount of protection. What I mean is that if you apply a product with an SPF of 20 at only 1.0 mg/cm^2, you’ll be getting an SPF of 10, and that’s assuming that amount is enough to form an even layer on your skin. You may not even be able to cover your face completely with that much. Remember, your skin as mountains and valleys and 2.0 mg/cm^2 is required to achieve a reliably even layer. ”

    This is not true. The relationship between application amount and SPF is not linear. I could provide numerous references to support my claim. Here is one:
    J Am Acad Dermatol. 2003 Jan;48(1):1-19
    Cutaneous photodamage, oxidative stress, and topical antioxidant protection.
    Pinnell SR.
    Full text can be accessed online at
    It is an excellent article by Sheldon Pinnell. See page four of the article which has a very nice chart for various SPFs and application amounts.

  • Eileen

    I got such a chuckle out of reading all the brouhaha about measurements and particularly your cheeky comment 😉 about Americans wanting it in teaspoons. When I first started wearing sunscreen in 1960, you could only buy it from a pharmacy and it usually had to be special ordered. It came with the direction to use “a spoonful” on the face and neck–not even any indication of what kind of spoon. How’s that for a scientific measurement? 🙂

  • Belle

    My face is so small lol! I calculated by tsp measurement, and it was only ~0.1998 tsp! How much would that be in a 1/4 tsp? Hopefully this means that I can use ~0.0500 less (:

  • Catarina

    Hi John,
    thank you for this another very informative post, like all of yours are! You are the person I have learned the most about sunscreen. Visualizing the amount of sunscreen one needs helps a lot. Because although I have seen this 2 mg/cm² often I have simply relied on using enough but obviously I don’t!

  • @Anne

    Ugh! I completely get what you mean. It drives me INSANE when people use the phrase, “A little goes a long way” to justify using anything expensive. It seriously annoys me. Just own up to the true reason why you like it: the packaging, the formulation, that you’re a makeup snob, your best friend recommended it, etc… Gah, people just need to be more honest!!

    Okay, sorry for MY rant. Lol! I have also heard that you can use less inorganic sunscreens than organic ones. But I have NEVER seen ANY data that even remotely suggests this. Furthermore, the omniscient and ubiquitously used BASF sunscreen simulator, does not make any kind of distinction in that aspect. Therefore, it seems prudent to just treat both types of sunscreens equally when it comes to application amount.

    As for your sunscreen’s texture, as long as it isn’t like a foam or anything, following the 1/4 teaspoon rule should be fine.

    Thanks for the support and the willingness to express your appreciation!

  • Anne

    Another great post by very knowledgable John! I wish it was required reading for anyone who wears SS as it drives me nuts when I read a review saying “oh, it seems expensive but it lasts FOREVER” when the size in question is 1fl oz. Or that the reviewer uses only a “drop” for her face…. arrggghhhh!

    Sorry for the rant 🙂 The visuals are really marvelous, so my question has been asked indirectly already – how does this impact a thick ZO based SS? I mix 2 – one that’s 23% ZO, another that’s 20% ZO to create my own “tinted” sunscreen. Both of them are very thick though one is fluffier than the other. Should I just follow the advice & squirt the correct amount into a 1/4 teaspoon ? I’ve read from dermatologists that if you use a ZO SS, there is some latitude to use a bit less… Is this wrong?

    I look forward to continue following you on your blog, thank you for the great service you are providing (and your great writing style!) Really a pleasure to read.

  • @Maggie

    Haha, American want it in teaspoons. Everyone else wants it using the metric system. I can’t seem to satisfy anyone lol! But, that’s a good idea.

    I admit the confusing part of the photo is that it doesn’t show the sunscreen’s thickness. It’s spread out quite a bit in the palm of my hand, as noted by the finger marks. 🙂

    But anyways, thanks for reading and commenting!

  • Maggie

    Hmm…judging by the comments, you NEED to add something to your post: a statement that the amount you calculated is approximately 1/4 teaspoon along with a photo of a 1/4 teaspoon in your hand. Thinking of the amount as 1/4 tsp will make more sense to a lot of Americans who use only vaguely remember chemistry but have grown up around around kitchen tools.

    That photo with the white goop is VERY misleading–what if your reader had larger hands than you? I thought it was weird when your first commentator, Anna, claimed she uses 4-5 pumps of Supergoop for the face and STILL insisted that it was merely 1/10 of what you used in the photo. I mean, I would hope it won’t take 40 pumps to get approximately 1/4 tsp worth of product out.

    Aside from that, I was grateful and very much relieved for your math and your post: depending on who was talking, I’ve always been told that ideally, 1/2 tsp or 1 tsp should be used for the face–that’s double or quadruple the amount you calculated here. For anyone who tells me otherwise–I will direct them here. =D

  • @Nicholas

    Haha! That made me snort. 😉 Yeah, just do the best that you can, and make note of how much UVA protection your sunscreen provides as well.

  • Nicholas

    That much sunscreen makes me feel claustrophobic. I use a spf 30 – 50, apply liberally and hope for the best.

  • @Sarah

    That’s a good idea, to apply two layers of sunscreen in order to achieve the correct amount! I’m going to put your idea into the article, because that’s a viable option. 🙂

    As for using two layers of different types of sunscreen, as long as you’re not actually mixing them together, that’ll be fine! Just let the first one set, and then gently apply the second one. There will be some mixing, but hopefully not enough to negatively impact either. I’d like to note that both types of sunscreens “sit” on your skin. Organic ones doesn’t have to absorb into your skin in order to work. 🙂

    Thanks for commenting!

  • @Firn

    Yay, glad you learned something!

    As for mixing a foundation into an organic sunscreen… well, you can certainly do it. But from my experience, organic UV filters are much more temperamental than inorganic UV ones, in the sense that the former compounds are more largely influenced by the vehicle in which they are suspended. So by mixing in another product, you’ll be altering the vehicle.

    I personally wouldn’t recommend doing so, but if you must, consider applying a powder on top that contains a lot of inorganic-based sun protection. Well in your case, only ones that contain TiO2, since you appear to be allergic to ZnO. Something like this (with 15.3% TiO2) would work:

    Also, which foundation are you using to make your mixture? Because if that contains TiO2 as well, that would boost overall levels of protection as well, albeit not evenly.

    Does that make sense?

  • Sarah

    Thanks John for another great post. I’m sad to see you go, but I’m most definitely looking forward to reading many more interesting articles on your own blog.

    With applying sunscreen, instead of applying the entire approx. 1.2439ml in one sitting. I find that I have to split it up and apply it in two separate layers. It’s a lot of hassle, but I usually apply one layer first, wait for it to be absorbed, and then apply the next. It is the only way that I can tolerate it. Maybe it’s all in my mind, but I find it easier to “swallow” if I do it that way.

    Another question I always wanted to do, are there any negative effects if I combine a chemical sunscreen with a physical one? Say, if I want to apply a chemical one first, let that sink in, so that it’s effectively “in my system”; and then apply another layer, only this time, it is a physical one, so that it “sits” on top of my skin, forming a protective layer. Would they actually compromise each other?

    Many thanks again. I love reading your answers to other readers’ questions! I can always learn something from it.

  • Firn

    At long last, the answer to the mysterious dosage of 2mg/cm2! I am allergic to ZnO sadly so I have to rely on chemical sunscreens.

    How would mixing in a foundation in a ratio of 1:3 affect my SPF and application? I am doing this to thin out the formulation and colour correct.


  • @Kat

    Haha I get where you’re coming from. However, even if I used the metric system (note that I do use mLs), it’d be even more difficult for people to comprehend their facial surface area in meters^2. Centimers are too small, and who actually uses decameters these days? Maybe I’m being biased, but I used the most logical units in my opinion.

  • @janine

    Lol! I thought the photos would help. 😉 Still, I’d be happy to walk you through the calculations if you’d like.

  • @Lucas

    Yes, the density can have an influence. However, not enough to make a big difference. And besides, there’s no reliable way for the average consumer to calculate the actual density of a sunscreen. And I doubt manufacturers/companies would be willing to release that information. If they do, you can go ahead and use that data to alter your calculations.

  • @rozy

    How come the post didn’t make sense to you? I’d be happy to explain the math. 🙂

  • @Anna

    The 2.0 mg/cm^2 comes from the FDA! 🙂 They require that amount for all testing for all SPF ratings using the indoor COLIPA system.

    Yeah, I know it’s a lot sunscreen, but there are ways to help tolerate that amount. For example, use an alcohol-based makeup setting spray, or mix in a bit of foundation that contains alcohol. This will really help thin, and dry out the overall texture.

    As for applying half the amount of sunscreen, you will then get half the amount of protection. What I mean is that if you apply a product with an SPF of 20 at only 1.0 mg/cm^2, you’ll be getting an SPF of 10, and that’s assuming that amount is enough to form an even layer on your skin. You may not even be able to cover your face completely with that much. Remember, your skin as mountains and valleys and 2.0 mg/cm^2 is required to achieve a reliably even layer.

    Does that make sense?

  • Kat

    Convert into units you can understand… ft & oz?! Jeebus America adopt the metric system already! You wouldn’t need conversion charts if you cooked by metric weight instead of crazy volumes. But seriously, thanks for this post John, it’s really useful, as have been all your posts. I’ll look forward to reading more on your own blog 🙂

  • janine

    Thank God for those photos at the bottom, ‘cuz prior to that I was L-O-S-T.

    Great info, though. Thanks.

  • Lucas

    I really enjoyed this and went measure my face. haha
    It’s really a lot of sunscreen! But isn’t density also important? Because isn’t the 1g = ~1mL true for water, which is less dense than most sunscreen lotion?


  • rozy

    I really like the banana boat baby sunscreen, im allergic to octcocrylene but I still wanted a chemical sunscreen so its a bit greasy but it doesnt make my skin burn AT ALL which a lot of chemical sunblocks do, I also use the new Natural Reflect Baby by them has mostly zinc unlike most cheaper physical sunblocks and titanium tends to sting me a little bit but this mostly zinc based one didnt. Also I took math support and this post made no sense. But I get the general message that most people do not put on enough sunscreen.

  • Anna

    OOPS – I meant that I’m leaning toward the FORMER, i.e. that you’re right and Supergoop! is being subversive, not the other way around!

  • Anna

    Interesting. I had just been wondering this, since I have a thing of Supergoop! City Sunscreen Serum that says “apply 1-2 pumps over face and neck daily”, which seems like virtually nothing and in no way goes far enough to moisturize my face, let alone provide sun protection. I use 4-5 pumps, which is about one tenth of the liquid volume you show up there. So one of two things going on – either Supergoop is lowballing its required amount so far as to be completely irresponsible, or the 2mg/cm^2 figure is inaccurate. I’m leaning toward the latter and will adjust accordingly.

    Having said that, I have some questions:
    -where does the 2mg/cm^2 figure come from? Looking that your splodge of sunscreen up there, this is absolutely zero chance of that soaking into my face ever. It seems like a ridiculous amount of product and if that’s really what’s required, chemical sunscreen technology *sucks*.
    -if one applies less than the required amount – for the sake of argument, let’s say half that volume – then what is the consequent reduction in effective SPF?

    Cheers John!

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