About uv.today
uv.today does one thing: tell you how strong the sun is right now, at your location, in terms you can act on. No app to install, no account, no dark patterns.
Data source
UV index data (current and hourly forecast) comes fromOpen-Meteo, which derives it from atmospheric models including ozone column and cloud cover. City search uses Open-Meteo's geocoding API; the optional "use my location" place name uses BigDataCloud's reverse geocoder. Your coordinates are sent to those services to fetch data and are not stored by us — your chosen location and skin type live only in your browser's local storage.
How time-to-sunburn is calculated
The UV index is defined so that an index of 1 equals 25 mW/m² of erythemally weighted irradiance. Dermatology literature assigns each Fitzpatrick skin type a typical minimal erythemal dose (MED) — the UV dose at which skin just begins to redden:
| Skin type | Typical MED |
|---|---|
| I — always burns, never tans | 200 J/m² |
| II — burns easily | 250 J/m² |
| III — sometimes burns | 350 J/m² |
| IV — rarely burns | 450 J/m² |
| V — very rarely burns | 600 J/m² |
| VI — almost never burns | 1000 J/m² |
Time to sunburn = MED ÷ irradiance. In minutes: MED × 40 ÷ UV index ÷ 60. Example: type II skin at UV 8 → 250 × 40 ÷ 8 ÷ 60 ≈ 21 minutes.
What the estimate doesn't capture
- Reflection: water, sand, and especially snow can nearly double effective UV.
- Altitude: roughly +10% UV per 1,000 m of elevation.
- Medications and conditions that increase photosensitivity (see our guide).
- Individual variation — MED values are population-typical, not personal measurements.
Treat burn times as planning estimates, not precision instruments, and round down when it matters. uv.today provides general information, not medical advice.
Contact
Questions, corrections, or partnership ideas: hello@uv.today