What does the UV index mean?
The UV index measures the level of ultraviolet radiation at the Earth's surface. It starts at zero and has no fixed upper limit. The higher the number, the greater the potential for damage to skin and eyes and the less time harm can take.
Official UV exposure categories
- 0–2: Low. Protection is normally not required.
- 3–5: Moderate. Protection is required.
- 6–7: High. Protection is required.
- 8–10: Very high. Extra protection is required.
- 11+: Extreme. Extra protection is required.
WHO recommends sun protection when the UV index is 3 or higher: seek shade around midday, wear covering clothing, a broad-brimmed hat and sunglasses, and use broad-spectrum sunscreen on skin that cannot be covered.
Clouds do not remove UV risk
UV can remain high under cloud, and reflection from water, sand and fresh snow can increase exposure. Use the forecast UVI and current conditions together, especially during the hours around solar noon.
Frequently asked questions
At what UV index do I need protection?
WHO recommends protection when the UV index reaches 3 or higher.
Can the UV index be higher than 11?
Yes. The scale starts at zero and is open-ended; 11 and above is classified as extreme.
Can UV be high on a cloudy day?
Yes. Clouds do not block all ultraviolet radiation, and some cloud conditions can still allow high surface UV levels.
Method and sources
Last reviewed: July 11, 2026.
