☀️ UV Index Checker
Check the current UV index for any location. Get sun protection recommendations based on UV levels. Powered by Open-Meteo API. Free — no signup.
What UV Index Checker Does
This tool reports the ultraviolet index for a place: the peak expected today, the reading at the current moment, and the risk category each falls into.
The distinction between those two numbers matters more than it sounds. A UV forecast headline is almost always the day's maximum, which occurs around solar noon. Check at nine in the morning or five in the afternoon and the actual figure can be a fraction of it — so a page showing only the peak tells an evening visitor their risk is far higher than it is.
The index itself is a standardized international scale, not a percentage or a temperature. It is open-ended, roughly linear in burning potential, and deliberately the same in every country — which makes it one of the few environmental numbers that means the same thing wherever you read it.
How to Use UV Index Checker
- Enter a city name or coordinates
- Click "Check UV" to get the current UV index
- View the UV level and protection recommendations
- Plan outdoor activities based on UV forecast
Formula Used by UV Index Checker
What the categories are
Low 0–2, Moderate 3–5, High 6–7, Very High 8–10, Extreme 11+
- the scale
- The WHO Global Solar UV Index, adopted internationally and used unchanged by the EPA
- open-ended
- There is no maximum. Readings above 11 occur at altitude and in the tropics
Worked example
Peak UV measured live on 11 September 2026 at five latitudes.
- Quito, on the equator at 2,850 m: 8.3 — Very High
- Miami: 7.65 — High
- Sydney, in early spring: 5.1 — Moderate
- London: 2.65 — Low
- Reykjavik: 2.8 — Low
Result: A threefold spread on the same day. Latitude and season dominate, and altitude adds on top — Quito is high partly because it is on the equator and partly because it sits well above 2,500 meters.
How much cloud actually removes
attenuation = 1 − (forecast UV ÷ clear-sky UV)
- clear-sky UV
- What the index would be with no cloud at all — a separate figure the model produces
Worked example
The same five locations, comparing forecast against clear-sky peak.
- London: 2.65 against 4.7 clear-sky
- 1 − (2.65 ÷ 4.7) = 0.44
Result: Cloud removed 44% of London's UV that day. Miami lost 8%, Reykjavik 8%, Sydney 18%, Quito 16%. Heavy cloud matters; light cloud removes far less than people assume, which is why overcast days still burn.
The WHO Global Solar UV Index
The same categories worldwide. Protection advice is the internationally published guidance for each band.
| Index | Category | Protection |
|---|---|---|
| 0–2 | Low | No protection needed for most people |
| 3–5 | Moderate | Seek shade near midday; sunscreen and a hat |
| 6–7 | High | Protection required — SPF 30+, hat, sunglasses, shade |
| 8–10 | Very High | Extra protection; avoid the sun between 10am and 4pm |
| 11+ | Extreme | Take all precautions; unprotected skin can burn in minutes |
Measured Live: Peak UV and What Cloud Took Off It
Queried 11 September 2026. The clear-sky column is what the index would have been with no cloud, which is how the attenuation is calculated.
| Location | Peak UV today | Clear-sky peak | Removed by cloud | Category |
|---|---|---|---|---|
| Quito (equator, 2,850 m) | 8.3 | 9.9 | 16% | Very High |
| Miami | 7.65 | 8.3 | 8% | High |
| Sydney | 5.1 | 6.2 | 18% | Moderate |
| Reykjavik | 2.8 | 3.05 | 8% | Low |
| London | 2.65 | 4.7 | 44% | Low |
How to Read Your Result
Peak is not now
The number most UV pages headline is the daily maximum, reached within an hour or so of solar noon. UV falls away steeply either side of it — far more steeply than daylight does, because the sun's angle determines how much atmosphere the radiation crosses. A day with a peak of 8 is genuinely Very High at one in the afternoon and can be near zero by six. This tool shows both figures for that reason, and the current one is the one to act on.
UV has almost nothing to do with temperature
The most common misjudgement about sun exposure is treating heat as the warning signal. UV is driven by solar angle, ozone, altitude and cloud; temperature is driven by entirely different things. A clear, cold spring day at altitude can carry a higher index than a hazy, sweltering afternoon in August, and snow makes it worse by reflecting UV back up at you. If you are judging by how warm it feels, you are reading the wrong instrument.
Cloud is unreliable protection
The measurements above span 8% to 44% attenuation on the same day across five cities. Thin or broken cloud can remove very little, and scattered cloud occasionally produces brief readings above the clear-sky value through edge-of-cloud reflection. The practical consequence is familiar: overcast days produce plenty of sunburn, because people judge exposure by brightness and glare rather than by the index.
Altitude and surface push it up
UV rises roughly 10-12% per 1,000 meters of elevation, which is part of why Quito reads higher than Miami despite similar latitude advantages. Reflective surfaces add more: fresh snow can bounce back most of the UV striking it, water and pale sand a meaningful fraction. Mountains in winter combine thin atmosphere with snow, which is why high-altitude skiing produces sunburn in conditions that feel nothing like beach weather.
Limitations & Accuracy Notes
- Forecast model output, not a ground measurement. It cannot see local shading, pollution haze, or the exact spot you are standing in.
- Shows today only — the peak and the current reading. There is no hourly curve, no multi-day forecast, and no time-of-peak.
- The clear-sky comparison used in the table above is not displayed in the tool itself, though the API returns it.
- No altitude or surface-reflection adjustment beyond whatever the model already accounts for, and no personal risk estimate.
- Place-name search resolves to one coordinate, so a large or mountainous area is represented by a single point.
- The category advice is the published WHO/EPA guidance for each band, not a recommendation tailored to skin type. For exposure time by skin type, see the UV index and vitamin D calculator.
- Not medical advice, and no index value is a safe threshold — UV damage accumulates and there is no exposure at which risk is zero.
Frequently Asked Questions
What is the UV index?
At what UV index is sun protection required?
What does the UV index number mean?
Why do you show clear-sky UV as well?
Does the index change through the day?
Does altitude or snow affect it?
Can I get sunburnt through a window?
Is this medical advice?
References & Further Reading
- World Health Organization — Global Solar UV Index: A Practical Guide — The international standard defining the index, its categories and the protection advice attached to each band
- US EPA — UV Index Scale — The US presentation of the same scale, with the federal protection recommendations quoted in the category table
- Open-Meteo — Air Quality API documentation (UV index variables) — Documents the uv_index and uv_index_clear_sky variables this tool reads, and the CAMS model behind them