Sunscreen Amount Calculator
Tick the areas you’re covering and see how much sunscreen it really takes to hit the dermatologist’s 2 mg/cm² standard — in grams, teaspoons, and shot glasses, per coat and for the whole day.
How much to use
Based on the dermatology standard of 2 mg/cm². Most people apply a quarter to half of this — using too little is the same as buying a much lower SPF.
The amount is the part everyone skips
When a sunscreen is tested for its SPF, technicians spread a specific, generous amount over the skin: two milligrams for every square centimetre. That is the amount the number on the bottle is promising to deliver. Apply less — as almost everyone does — and you get less protection, often dramatically less, because SPF and quantity don’t fall together in a straight line.
Seeing the real figure in teaspoons or shot glasses makes it concrete. A whole adult body needs roughly a shot glass per coat; a face and neck need about a teaspoon. If a small bottle is lasting you the whole summer, that’s a sign you’re under-applying, and a higher SPF won’t make up the difference.
Frequently Asked Questions
Where does the 2 mg/cm² figure come from?
That's the application density used when sunscreens are tested for their SPF rating. To actually get the SPF on the label, you have to apply the same amount that was used in the lab — about 2 milligrams of product per square centimetre of skin.
How much is that for a whole body?
For an average adult covering all exposed skin, it works out to roughly 30–35 grams per application — about a shot glass full, or a rounded teaspoon for the face and neck alone. Most people apply a quarter to a half of that, which is why real-world protection often falls well short.
Why does using too little matter so much?
SPF doesn't fall off in a straight line with the amount you apply. Studies suggest that using half the tested amount can leave you with only a fraction of the labelled SPF. Applying a generous, even layer is one of the most important things you can do — more so than chasing a higher number on the bottle.
Is the body-area estimate exact?
No. It uses the 'rule of nines', a standard way of splitting adult body surface into rough percentages, applied to an average 1.8 m² body. Real bodies differ, so adjust the surface-area figure for children or different builds and treat the result as a practical guide.
General guidance only, not medical or dermatological advice. Follow your product’s label and see a professional about your own skin.