Sunscreen Calculator
Enter the people, the days of sun, how many applications a day the swimming schedule demands, and your bottle size. The calculator gives the ounces to pack and the bottles to buy.
The full-body adult dose is one ounce - a shot glass - per application, and most people apply a quarter to half of that, which quietly turns SPF 50 into SPF 3 by the time the beach starts. Sprays are the worst offenders: half the can lands in the wind. Reapply every two hours and after every towel.
How to use
- Count people and sun days honestly - naps by the pool count.
- Swim days mean reapplication every two hours, three-plus a day.
- Pack one more bottle than the math; the store at the beach knows.
Frequently asked questions
How much sunscreen do I need for a week at the beach?
One person applying properly uses about an ounce a day on beach days - 7 ounces for the week, nearly a full 8-ounce bottle each. A family of four goes through most of a gallon-jug-sized stash.
How much sunscreen should I apply?
One ounce, a full shot glass, for an adult body - and half a teaspoon for the face and ears. Most people apply a quarter to half of that, which cuts SPF 50 down to roughly SPF 3 in practice.
Do spray sunscreens work?
They work if used generously: hold close, spray until the skin glistens, then rub in. Half of a casual spray lands in the wind, which is why sprays are the classic under-application trap - especially on kids.
How often should sunscreen be reapplied?
Every two hours, and after swimming, sweating or toweling - water resistant does not mean towel resistant. The calculator counts reapplications into the supply so the bottle does not run out on day four.