Uv Exposure Time
Calculator
Results
- Time to sunburn (minutes)
- 20.833333
- Time to sunburn (seconds)
- 1,250
- Erythemal irradiance (W/m²)
- 0.2
Weather results
| Time to sunburn (minutes) | 20.833333 |
| Time to sunburn (seconds) | 1,250 |
| Erythemal irradiance (W/m²) | 0.2 |
formula-map diagram
- Time to sunburn (minutes)
- 20.833333
- Time to sunburn (seconds)
- 1,250
- Erythemal irradiance (W/m²)
- 0.2
Weather relationship
Formula
t = MED × SPF ÷ (UVI × 0.025 W/m²) (1 UV index unit = 25 mW/m² erythemal irradiance)= 20.833333333333
Note
This is a simplified model: it applies the published standard formula to the numbers you entered and ignores local terrain, radiation, precipitation type and instrument error. Wind chill is the 2001 NWS/Environment Canada regression, valid at or below 10 °C with wind at or above 4.8 km/h; the heat index is the Rothfusz regression, reliable above about 27 °C; dew point uses the Magnus approximation (a = 17.27, b = 237.7 °C) over liquid water; wet bulb uses Stull's approximation at standard sea-level pressure; pressure and density altitude assume the International Standard Atmosphere and dry air. Do not use these results for aviation, structural or safety decisions without an official forecast or a qualified professional.
More in Weather and climate
See all →Frequently asked questions
How does this calculator estimate safe sun exposure time?+
It combines the current UV index with a skin type's typical time-to-burn baseline to estimate how long unprotected skin can be exposed before reaching a sunburn threshold, since a higher UV index shortens that safe window roughly in proportion to its intensity.
Why does skin type change the calculated exposure time so much?+
Skin types with more natural melanin protection (often categorized on the Fitzpatrick scale) tolerate meaningfully longer UV exposure before burning than fair skin types, so the same UV index and exposure duration can be safe for one skin type and cause sunburn in another.
Why does UV index matter more than air temperature or how hot it feels?+
UV radiation intensity isn't reliably indicated by temperature or visible brightness; a cool, hazy, or overcast day at high altitude or high latitude in summer can still carry a high UV index, so relying on how hot or sunny it 'feels' is an unreliable way to judge burn risk.
Does sunscreen change the calculated safe exposure time proportionally to its SPF number?+
Roughly, yes: SPF is defined as a multiplier on time-to-burn when applied correctly at the recommended thickness, so SPF 30 theoretically extends safe exposure about 30-fold versus bare skin, though in practice under-application and sweating or swimming reduce this considerably from the label value.
Why does exposure time need reassessing throughout the day?+
UV index isn't constant; it peaks around solar noon and is lower in early morning and late afternoon as the sun's angle changes, so a 'safe' exposure duration calculated at one time of day can be too long or unnecessarily conservative just a few hours later.