How Much Sunscreen You Need to Be Using - With Calculator!


I bet you’re putting on sunscreen wrong. Let me show you. Oh and I built a cool free tool for you that I’ll show you soon.

What most people don’t realize is that how MUCH you use actually matters more than the SPF.

SPF is the multiplier of how much longer you can spend in the sun but get the same UV dose. But EVERY sunscreen gets its number by being tested at a set THICKNESS of 2 mg / square cm of skin surface area.

This graph shows the effective SPF you’re getting if you use a thinner coating.

At half the official thickness, SPF 50 becomes SPF 7. 30 Becomes 5.5. This is WHY people often still burn when wearing sunscreen. Studies have shown that the amount most people instinctively use is between 1/4 and 1/2 the official thickness (some are advocating that the FDA change its testing protocol accordingly).

Show how much SHOULD you be using? Let me show you.

I activated my nerd powers and calculated the surface area of my face and neck, which translates to roughly 2g of sunscreen required. Measuring using my jewelry scale gives a little over 1/3 tsp.

But doing my whole body would take 37g, or 6tsp. That’s 2/3rd of this whole bottle.

That’s why I use different stuff for my face and for the rest of my body.

Want to know your sunscreen measurements? I built a handy dandy calculator for you on my website. It shows you how much you need for each part of your body. Go check it out.

And follow for next time, when i’ll show you how to best apply sunscreen and dispel some more common myths.

Sunscreen Surface Area Calculator

Remember, this calculated amount assumes that you’re using a good sunscreen! Check out below for my top recommendations.

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Sunscreens I Use

Full Body Sunscreen - UVA + UVB - German - The US standard for “broad spectrum” protection is pretty terrible. This one has the best European rating, at a great price!

Full Body Sunscreen - Broad Spectrum Mineral - Australian - For those who want a fully mineral, non-chemical option with a good price and nice texture. BONUS: It’s got a super cool bottle that changes color in the presence of harmful UV! 😎

Face Sunscreen - UVA/UVB - Sensitive Skin - This is a bit pricey for full-body application, but sometimes for the face it's worth going higher-quality. This broad-spectrum sunscreen has added Hyaluronic Acid, Caffeine, and green tea polyphenols for added hydration, skin tightening, and anti-oxidative effects.

(note: these are affiliate links–I have no relationship with the brand, but your using these links earns me a small commission on each purchase, at no added cost to you. Every little bit helps me keep putting out this content! 😄)


Calculation of sunscreen application thickness REF

Schlich formula for body surface area calculations