Key points
- The Global Solar UV Index runs from 0 upward: 0–2 Low, 3–5 Moderate, 6–7 High, 8–10 Very High, 11+ Extreme (WHO/WMO/UNEP).
- The index depends on sun elevation, latitude, cloud cover, altitude, ozone and ground reflection — not on temperature.
- The official WHO protection messages are shade during midday hours, a shirt, sunscreen, a hat and sunglasses.
- The index gives no skin-type times and no personal advice. It is a published number with an official band label.
Direct answer: The Global Solar UV Index is a single number, from 0 upward, that describes how strong the sun’s ultraviolet radiation is at a place and time. It runs in five bands — Low, Moderate, High, Very High and Extreme — defined by WHO, the World Meteorological Organization and the United Nations Environment Programme. This article explains the bands, what moves the number, and how to check today’s index.
What the UV index is
Ultraviolet radiation is the part of sunlight that causes sunburn. The UV index turns the measured strength of that radiation into a number a general reader can follow, in the same way the Air Quality Index turns pollution measurements into a number. The scale was developed jointly by WHO, the World Meteorological Organization, the United Nations Environment Programme and the International Commission on Non-Ionizing Radiation Protection, and the same bands are used worldwide.
The bands
| UV index | Band | Official protection message (WHO/WMO/UNEP) |
|---|---|---|
| 0–2 | Low | Wear sunglasses on bright days; if you burn easily, cover up and use broad-spectrum sunscreen. |
| 3–5 | Moderate | Seek shade during midday hours; wear a shirt, sunscreen and a hat. |
| 6–7 | High | Seek shade during midday hours; wear a shirt, sunscreen and a hat, and wear sunglasses. |
| 8–10 | Very High | Seek shade during midday hours; wear a shirt, sunscreen and a hat, and wear sunglasses; take extra care — unprotected skin can burn quickly. |
| 11+ | Extreme | Take all precautions — seek shade, wear a shirt, sunscreen and a hat, and wear sunglasses; avoid being outside during midday hours. |
The messages are the official ones, worded for the general public. They are the same at every level of the scale in structure — shade, shirt, sunscreen, hat, sunglasses — with the urgency rising as the number rises.
What moves the number
The UV index is not the temperature, and it does not follow the weather forecast. It depends on the height of the sun in the sky, which is why it peaks around midday and in summer, and why it is higher near the equator than near the poles. Cloud cover reduces it but does not block it. Altitude raises it: the air is thinner higher up, so more UV gets through. Ozone in the upper atmosphere absorbs UV, so a thinner ozone layer means a higher index. And surfaces reflect it — snow, sand and water bounce UV back up, which is why the index can be high on a bright beach or a ski slope even when the air feels cool.
That is also why a cool day can be a high-UV day. Temperature comes from the air; UV comes from the sun’s position and the sky above it. The two move together often, but they are not the same thing.
How to check today’s index
The index is published as a forecast, not a live measurement. The Copernicus Atmosphere Monitoring Service publishes a global UV forecast that follows the WHO definition, and national weather services publish their own. The lookup tool on this site shows the published index for a place with its time and source. When quoting an index, give all three — the number, the time it applies to, and the source — because the number changes through the day as the sun rises and falls.
The phrase “UV index today” is one of the most searched UV phrases, and for good reason: the index is only useful on the day it applies to. Yesterday’s number says nothing about today.
What the index does not say
The UV index gives no skin-type times. It does not say how many minutes any person can spend in the sun, because that depends on skin type, clothing, sunscreen and behaviour — none of which the index measures. It gives no personal advice and no personal verdict. It is a published number with an official band label, and the protection messages are the general ones WHO publishes for everyone.
Frequently asked questions
Is the UV index the same as the temperature?
No. The UV index measures ultraviolet radiation, not heat. A cool, clear day at altitude can have a higher UV index than a hot, hazy day at sea level.
Does the UV index tell me how long I can stay in the sun?
No. It gives no skin-type times. It shows the published index and the official WHO scale message only.
Can the UV index be high on a cloudy day?
Yes. Cloud cover reduces UV, but it does not block it: a large share of UV passes through light cloud, so the index can still be Moderate or High.