An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

UV Index Scale

The UV Index scale used in the United States conforms with international guidelines for UVI reporting established by the World Health OrganizationExitLearn how to read the UV index Scale to help you avoid harmful exposure to UV radiation.


0 to 2: Low

UV Index Low - Green
No protection needed. You can safely stay outside using minimal sun protection.

3 to 7: Moderate to High

UV Index Moderate - YellowUV Index High - Orange

Protection needed. Seek shade during late morning through mid-afternoon. When outside, generously apply broad-spectrum SPF-15 or higher sunscreen on exposed skin, and wear protective clothing, a wide-brimmed hat, and sunglasses.

8+: Very High to Extreme

UV Index Very High - RedUV Index Extreme - Purple

Extra protection needed. Be careful outside, especially during late morning through mid-afternoon. If your shadow is shorter than you, seek shade and wear protective clothing, a wide-brimmed hat, and sunglasses, and generously apply a minimum of  SPF-15, broad-spectrum sunscreen on exposed skin.

The Shadow Rule


An easy way to tell how much UV exposure you are getting is to look for your shadow:

  • If your shadow is taller than you are (in the early morning and late afternoon), your UV exposure is likely to be lower.
  • If your shadow is shorter than you are (around midday), you are being exposed to higher levels of UV radiation. Seek shade and protect your skin and eyes.