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SunGuard
SPF × baseline burn minutes = estimated protection window.
SPF is a multiplier on how long it takes your unprotected skin to burn — if you'd normally burn in 10 minutes, SPF 30 theoretically extends that to roughly 300 minutes, though real-world factors shrink this considerably.
Sweat, water, and simple time degrade sunscreen's effectiveness well before the theoretical window runs out — dermatologists generally recommend reapplying every 2 hours regardless of what the SPF math suggests.
Daily energy expenditure with personalised macro splits.
OpenBody mass index with healthy-range guidance.
OpenUS Navy circumference method for body fat percentage.
OpenDaily hydration target based on weight, activity, and climate.
OpenProtected time (minutes)
450
Reapply every 2 hours regardless — sweat and water rapidly reduce protection.
What you entered
SPF multiplier applied to unprotected burn time
30 × 15 min= 450 minResult
Protected time (minutes): 450
SPF 30 on skin that burns in 15 minutes theoretically protects for about 450 minutes — but reapply every 2 hours regardless.