What is the UV Index?

The UV Index is an EPA scale from 0 upward that forecasts how strong the sun's ultraviolet radiation will be at midday. Higher numbers mean faster skin and eye damage; it runs past 11 in the tropics and at altitude.

What are the UV Index levels?

Five: Low (2 and below), Moderate (3–5), High (6–7), Very High (8–10), and Extreme (11+), colored green, yellow, orange, red, and violet.

What UV Index is considered dangerous?

Any reading of 6 or higher is high enough to burn unprotected skin in minutes. At Very High (8+) and Extreme (11+), avoid the sun between 10 a.m. and 4 p.m.

Who creates the UV Index forecast?

In the United States the EPA and the National Weather Service issue it daily. The forecast estimates the clear-sky peak UV at solar noon using ozone, sun angle, elevation, and cloud cover.

Is a UV Index of 6 high?

Yes. A 6 falls in the High band, where unprotected skin can begin to burn in roughly 22 minutes. Wear sunscreen, a hat, and sunglasses, and seek shade at midday.

Does a low UV Index mean no risk?

At Low (2 and below) burn risk is small for most people, but reflective snow or water and high altitude can still add exposure. UV below 3 carries little burn risk.

UV Index Scale: What Low, Moderate, High, and Extreme Mean

The UV Index is a simple 0-to-11-plus scale that tells you how strong the sun's ultraviolet radiation will be around midday. The US EPA and the National Weather Service publish it as a daily forecast for locations across the country, so you can see at a glance whether sun protection is worth the bother. Higher numbers mean ultraviolet rays reach the ground faster and skin and eye damage builds more quickly.

The scale is open-ended. It sits near 0 on a dark winter morning and can run past 11 in the tropics or at high elevation. The EPA sorts the numbers into five categories, each with a color and a protection message. Knowing which band you are in matters more than the exact figure, because the advice changes at the band edges, not at every point.

The five UV Index categories

EPA groups the index into Low (2 and below), Moderate (3 to 5), High (6 to 7), Very High (8 to 10), and Extreme (11 and above). Each step up roughly doubles the message: at Low you need little protection, at Moderate you should cover up near midday, and from High onward unprotected skin burns in minutes rather than hours.

The colors run green, yellow, orange, red, then violet for Extreme. A reading of 6 or 7 is genuinely high, not a middling value, and an Extreme 11-plus day calls for staying out of the sun during the peak hours entirely.

How the daily UV forecast is built

The EPA forecast is a clear-sky estimate of the peak ultraviolet level expected at solar noon. The model combines the forecast amount of ozone overhead, the sun's angle for your latitude and the date, your elevation, and predicted cloud cover. Because it targets the midday peak, the number you see is the strongest UV expected that day, not an average across all daylight hours.

Forecast and measured UV can differ. Thick storm clouds can pull the real value below the forecast, while bright high cloud or reflective snow can nudge it above. CDC advises treating the daily index as a planning tool: when it reads 6 or higher, build protection into your day rather than waiting to feel a burn.

What protection each level calls for

At Low (2 or under) most people can stay outside safely. From Moderate (3 to 5) upward, wear SPF 30 broad-spectrum sunscreen, a hat, and sunglasses, and seek shade near midday. At Very High (8 to 10) and Extreme (11+), minimize sun between 10 a.m. and 4 p.m., reapply sunscreen every 2 hours, and cover up.

Why the same number feels different by place

Two cities can share a UV Index of 6 yet deliver different real-world exposure. Elevation raises ground-level UV by roughly 10% per 1,000 meters, and reflective surfaces add to it: fresh snow bounces back as much as 80% of incoming UV. Latitude matters too, with the strongest sun near the equator. The forecast index already folds in elevation and sun angle, but reflection off snow, sand, or water is extra exposure on top of the number.

Check your local UV index

UV is driven by latitude, elevation, and clear skies, so it runs hardest in the Sun Belt and the high mountain West. These metros see some of the country's strongest UV — check the current forecast for each, or look up any US city on the UV index hub:

Honolulu, HI UV index — A tropical latitude keeps the UV Index in the Very High to Extreme range for much of the year.
Miami, FL UV index — Low latitude and strong sun push midday UV to Extreme through the long summer.
Phoenix, AZ UV index — Desert sun and reliably clear skies produce some of the highest UV readings in the country.
Las Vegas, NV UV index — Clear desert skies keep midday UV very high from spring through fall.
El Paso, TX UV index — High-desert elevation and clear air raise UV well above the national average.
Albuquerque, NM UV index — Mile-high elevation and clear skies make for intense midday UV.

Frequently asked

What is the UV Index?: The UV Index is an EPA scale from 0 upward that forecasts how strong the sun's ultraviolet radiation will be at midday. Higher numbers mean faster skin and eye damage; it runs past 11 in the tropics and at altitude.
What are the UV Index levels?: Five: Low (2 and below), Moderate (3–5), High (6–7), Very High (8–10), and Extreme (11+), colored green, yellow, orange, red, and violet.
What UV Index is considered dangerous?: Any reading of 6 or higher is high enough to burn unprotected skin in minutes. At Very High (8+) and Extreme (11+), avoid the sun between 10 a.m. and 4 p.m.
Who creates the UV Index forecast?: In the United States the EPA and the National Weather Service issue it daily. The forecast estimates the clear-sky peak UV at solar noon using ozone, sun angle, elevation, and cloud cover.
Is a UV Index of 6 high?: Yes. A 6 falls in the High band, where unprotected skin can begin to burn in roughly 22 minutes. Wear sunscreen, a hat, and sunglasses, and seek shade at midday.
Does a low UV Index mean no risk?: At Low (2 and below) burn risk is small for most people, but reflective snow or water and high altitude can still add exposure. UV below 3 carries little burn risk.