How to Read the UV Index

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What the UV Index Number Means

The UV Index is a standardized scale developed by the World Health Organization (WHO) to measure the intensity of ultraviolet radiation at ground level. The scale starts at 0 (no UV) and has no upper limit — though values above 11 are classified as "Extreme." Higher numbers mean more UV radiation reaches your skin per minute, and your risk of sunburn and long-term skin damage increases faster. A UV Index of 8 is not just "a little worse" than 4 — at UV 8, a fair-skinned person (Type II) can burn in as little as 15-20 minutes. At UV 4, that same person has about 30-40 minutes of safe time.

Try it in the app:

Open SunUp and look at the large number in the center of the dashboard. That is your current UV Index.

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Pro tip:

UV can be high even on cloudy days. Clouds only block 20-30% of UV radiation — SunUp always shows the real-time value, not just sky color.