UV Index Safe-Exposure Calculator
Enter today’s UV index and your skin type to estimate how long bare skin can be out before it starts to burn — and how much extra time a sunscreen is designed to add.
Time to burn
The SPF figure is an ideal-lab estimate. In real use, people apply far less than the tested amount, so treat it as an upper bound and reapply.
How the estimate works
The UV index is defined directly from the strength of sunburn-causing UV, so it can be turned into a rough time-to-burn. Every skin type has a different threshold dose — the amount of UV it takes to redden — and dividing that threshold by the UV strength gives the minutes of exposure it represents. Double the UV index and you roughly halve the time; darker skin, with more melanin, gets a longer window.
It is only a starting point. Your real threshold depends on your individual skin, medications, recent exposure, and the exact conditions, and the sunscreen multiplier assumes far more product than most people ever apply. Use the number to plan a shade break, not to sit out to the last safe minute.
Frequently Asked Questions
What is the UV index?
The UV index is a standardised measure of the strength of sunburn-causing ultraviolet radiation at your location. It runs from 0 upward: below 3 is low, 3–5 moderate, 6–7 high, 8–10 very high, and 11+ extreme. It's published in most weather forecasts and peaks around solar noon.
Where do the skin types come from?
They're the Fitzpatrick phototypes, a six-point scale dermatologists use to describe how skin responds to sun — from Type I, which always burns and never tans, to Type VI, deeply pigmented skin that very rarely burns. Darker skin has more melanin and a higher natural tolerance, which is why the estimated time to burn is longer.
Is the 'SPF × time' figure reliable?
Treat it as an optimistic upper bound. It assumes the ideal 2 mg/cm² application used in lab testing, which almost nobody achieves in real life, and it ignores sweat, water, and rubbing. In practice you get a fraction of that, so reapply on the two-hour rule rather than trying to ride the multiplied number to its limit.
Does this account for altitude, water, or snow?
No — this tool uses the plain UV index. Reflective surfaces like water, sand, and snow, and higher altitude, all raise the real UV reaching your skin. For those conditions, use our Sunburn Risk Score, which folds them in.
General guidance only, not medical or dermatological advice. Skin varies widely; when in doubt, cover up and see a professional about your own skin.