How Much Sunscreen Should You Use? Face & Body Amounts (+ Calculator)
Most people who “use sunscreen every day” still get too little sun protection — not because their SPF is wrong, but because they apply a fraction of what the number on the bottle assumes. SPF 50 tested at a proper thickness can behave like SPF 15 when you rub in a thin layer. This guide fixes that with the amounts dermatologists actually use, plus a calculator that tells you how much to apply and how long your bottle should last.
Face needs about ¼ teaspoon (the “two-finger rule” — a line along your index and middle finger). Full body needs about 1 ounce (a shot glass). Reapply every 2 hours outdoors, and after swimming or sweating.
Sunscreen amount calculator
Pick what you’re covering and how often you reapply. You’ll get the daily amount and how long a bottle lasts — so you know if you’re actually protected.
Based on the dermatology standard of ~2 mg/cm². Applying less lowers the real SPF you get — thickness matters as much as the number.
The two-finger rule, explained
For the face and neck, squeeze sunscreen in two lines running from the base to the tip of your index and middle fingers. That’s roughly the ¼–½ teaspoon studies use — an easy way to hit the right amount without measuring spoons. If you’re using a spray or stick, that’s much harder to gauge, which is exactly why thin, uneven coverage is so common with them.
- A quick thin smear on the face
- Skipping ears, hairline, back of neck
- Never reapplying after the morning
- Two-finger line for face + neck
- Cover ears, hairline, hands
- Reapply every 2h outdoors
Frequently asked questions
Is SPF 30 enough, or do I need SPF 50?
SPF 30 blocks about 97% of UVB and SPF 50 about 98% — a small gap. What matters far more is applying enough and reapplying, which is where most people fall short.
Do I need sunscreen indoors?
UVA passes through window glass, so next to a sunny window, yes. Deep indoors and away from windows, the exposure is minimal.
How long before going outside should I apply it?
Give chemical sunscreens about 15 minutes to bind to the skin. Mineral (zinc or titanium) sunscreens start working on contact.
The SPF number only delivers if you apply enough. Use the two-finger rule for your face, a shot glass for your body, and reapply every couple of hours outdoors. If a bottle lasts you months of daily use, you’re almost certainly applying too little.