The UV Index Explained: What the Numbers Mean and the EPA Shadow Rule
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How we wrote this: A plain-English summary of the U.S. EPA's UV Index pages, checked October 29, 2026.
What the UV Index is
The EPA says the UV Index is a daily forecast of the expected intensity of ultraviolet radiation from the sun, on a scale of 1 to 11+. The U.S. scale follows World Health Organization reporting guidelines, so a UV Index of 8 means the same thing in other countries that use it.
The levels and what to do
| UV Index | EPA level | EPA advice |
|---|---|---|
| 1–2 | Low | No protection needed. You can safely stay outside with minimal sun protection. |
| 3–7 | Moderate to High | Protection needed. Seek shade from late morning through mid-afternoon. Apply broad-spectrum SPF 15+ sunscreen generously, and wear protective clothing, a wide-brimmed hat and sunglasses. |
| 8+ | Very High to Extreme | Extra protection needed. Be careful outside, especially late morning through mid-afternoon. If your shadow is shorter than you, seek shade, cover up, and apply broad-spectrum SPF 15+ generously. |
The shadow rule
The EPA's quick test needs no app:
- Shadow taller than you (early morning, late afternoon): UV exposure is likely lower.
- Shadow shorter than you (around midday): you're getting higher UV. Seek shade and protect your skin and eyes.
It works anywhere, including winter ski slopes and cloudy beach days.
Find your forecast
The EPA publishes UV Index forecasts by ZIP code or city through its Envirofacts site. Check it with the weather before a beach day, then follow the beach day sun protection checklist and our guide to reading sunscreen labels.
Also see heat index and heat safety.