How much sunscreen do you need?

There comes a time in the life of every sunscreen geek when they’re ready to measure their face…

I’ll explain why, and give you all the tools you need to figure out how much SPF you need to properly safe your skin from harmful UV rays.

Whenever I write about weighing the sunscreen I use on scales, I usually get laughed at. Whenever we show a sunscreen that’s impossible to apply in larger amounts, we’ll get comments to just use less.

The amount of sunscreen to use to actually be safe from UV rays is difficult to gauge as a consumer. Brands will weasel out of the issue, telling you to use a “sufficient” amount, using anything from coins to pearls to hazelnuts as a comparative size. And then, there’re numbers floating around on the internet: one teaspoon, half a teaspoon, one gram, 0.4 ounces, two finger lengths. What?!

Sunscreen tests and SPF numbers

So, where does this come from?

When sunscreen is tested in independent labs to determine the SPF, they use 2 milligrams of sunscreen per centimetre of skin (2 mg/cm²). That translates to ¼ teaspoon for the average adult face, and 35ml for a full adult body. It is also more than most people intuitively apply. On top of that, it means that if you use less, you won’t reap the SPF printed on the bottle.

If you now think: no worries, I just use that super thick and oily SPF100 (or 80, or 50) and apply half of the recommended amount and still have 50% of that protection – no. This is not how sunscreen works, for mainly two reasons: first and foremost, the human skin isn’t smooth. It has bumps, dips, lines and pores, and the less sunscreen you apply, the higher the risk that you don’t end up with an even layer of sunscreen. (More at Michelle’s.)

Second, from what we know today, it’s not proven that sun protection diminishes linearly, meaning “half the amount of SPF50” doesn’t automatically equals SPF25. It could be. But also, it could not.

What we learned from this: ¼ tsp is the average amount of sunscreen you should apply to your face alone.

But: how much is ¼ teaspoon?!

When it makes sense to weigh your sunscreen

Especially when using a new sunscreen for the first time, it’s really easy to misjudge the amount you might need. This happens to me often with a very liquid or a mousse texture. Also, the weight of a sunscreen might differentiate dramatically while the volume (¼ tsp) LOOKS the same. That’s the reason why I hate when sunscreen brands tell you to use a “grape-sized” (or whatever comparison) amount. This is a bogus measurement: what is that supposed to look like?! Also, am I alone in finding it impossible to figure out the amount of SPF with a regular teaspoon?! (Teaspoons also come in very different sizes.)

So, here’s why and when I weigh sunscreen on scales: when I pull out a new sunscreen and one with a texture that makes it hard to eye-ball the correct amount. I don’t do that every day, obviously. But I also compare and try to find out how much of that correct amount will fit into my little ¼ tsp measuring tool.

How much SPF you really need?!

Above, we’ve been talking about “average” faces (and bodies). I don’t have to remind you that the human being comes in all shapes and sizes, which also can differ dramatically from average. Coincidentally I know my hat size (which is large), which always lets me suspect that I shouldn’t err below 1.4g when applying sunscreen.

I was curious though: and that was when I looked into measuring my face. There’re a lot of methods floating around on the web: I opted for the quick and dirty (more about the mathematical formula in German here). I pulled out a measuring tape and measured the width and height of my face.

Here’s the formula: Height x Width / 2 * 3,14 / 1000

My face is roughly 775cm2, which then means I should apply 1.6g of sunscreen actually!

MIND BLOWN.

“You’re just a control freak”

Look, I personally don’t care how much SPF you use. I just want to give you some pointers on how to figure out that amount on your own.

I personally find it most helpful to weigh my sunscreen on scales occasionally to check in on the amount and use the little measuring tool for very liquid formulas. Why? Because I want to reap the full protection of my SPF50, because hyperpigmentation is a bitch and difficult to treat, and skin cancer is no joke at all. It’s totally possible to use that amount when you find a sunscreen that works for you, too! (Check our sunscreen reviews, we tested around 30 sunscreens in the last 18 months.)