Free UV index calculator. Estimate safe sun exposure time, sunburn risk, and SPF recommendations based on UV index and your Fitzpatrick skin type.
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The UV Index measures the strength of ultraviolet radiation from the sun. Our calculator uses the WHO/WMO standard UV index scale and Fitzpatrick skin type classification to estimate how long you can safely stay in the sun without protection, and what SPF level you need.
The UV Index is an international standard measurement developed by the WHO and WMO. It ranges from 0 (nighttime) to 11+ (extreme). The scale is linear - UV Index 10 is twice as intense as UV Index 5. Higher values mean faster potential for sunburn and skin damage.
Time to Burn Formula
t = (MED × 16.67) / UV IndexKnow exactly how long you can stay outside before risking skin damage.
Get enough sun for vitamin D production without overexposure.
Select appropriate sunscreen protection for current UV conditions.
Plan sun exposure at the beach where reflection can increase UV by 50%.
Account for altitude and snow reflection in mountain environments.
Athletes can time training to avoid peak UV hours.
Prepare for different UV levels in tropical or high-altitude destinations.
At UV Index 0-2 (Low), most people can safely stay outside with minimal protection. At UV Index 3+ (Moderate and above), sunscreen, hats, and protective clothing are recommended, especially for fair-skinned individuals.
The Fitzpatrick scale classifies skin into 6 types based on how it reacts to sun exposure: Type I always burns (very fair), Type VI rarely burns (very dark). Your skin type determines your minimal erythemal dose (MED) - the UV exposure that causes minimal redness.
Not exactly. SPF 15 blocks about 93% of UVB rays, SPF 30 blocks 97%, and SPF 50 blocks 98%. The difference between SPF 30 and 50 is minimal. More important is applying enough sunscreen and reapplying every 2 hours.
UV radiation increases approximately 10-12% for every 1,000 meters (3,300 feet) of altitude gain. Less atmosphere means less UV absorption. At 3,000m, you could receive 30% more UV than at sea level.