The UV index scale
The UV index runs from 0 upwards in five bands: low (0–2), moderate (3–5), high (6–7), very high (8–10) and extreme (11+). One point equals 25 mW/m² of sunburn-weighted radiation. For fair skin, each point roughly halves your time: 56 min at UV 3, 28 min at UV 6, 15 min at UV 11.
The five bands
| Range | Band | Guidance |
|---|---|---|
| 0–2 | Low | No protection needed for most people. Too weak to build a tan. |
| 3–5 | Moderate | Seek shade near midday. Sunscreen for fair skin. |
| 6–7 | High | Protection required. Fair skin burns in under 20 minutes. |
| 8–10 | Very high | Extra protection. Avoid the sun between 11:00 and 15:00. |
| 11+ | Extreme | Unprotected skin burns in minutes. Stay indoors around midday. |
The WHO recommends sun protection from UV 3 upward, for every skin type. No level of the scale is an all-clear — the times below say how fast, not whether.
Level by level
| UV | Band | Type II | Type VI | Where you meet it |
|---|---|---|---|---|
| UV 1 | Low | 2 h 47 | 6 h 40 | A British or Irish midday between November and January, the first hour after sunrise in July, or any overcast winter afternoon. |
| UV 2 | Low | 83 min | 3 h 20 | A clear UK midday in March or October, an August evening around 18:00 in southern Europe, or a heavily overcast summer day almost anywhere. |
| UV 3 | Moderate | 56 min | 2 h 13 | A cloudy summer midday in the UK and Ireland, a clear day in early April at 50°N, or mid-winter in Sydney and Cape Town. |
| UV 4 | Moderate | 42 min | 1 h 40 | A bright late-April day in northern Europe, a Canadian summer morning around 10:00, or a July midday in Cape Town. |
| UV 5 | Moderate | 33 min | 80 min | The typical clear-sky ceiling of a British summer, a Melbourne day in October, or a Johannesburg winter midday — altitude alone adds around 21% there. |
| UV 6 | High | 28 min | 67 min | Southern Europe in May, the Australian spring, the South African highveld in September, or a UK heatwave at the summer solstice. |
| UV 7 | High | 24 min | 57 min | The clearest June days in the south of England, a normal summer midday in Madrid or Rome, or an Auckland day in December. |
| UV 8 | Very high | 21 min | 50 min | Mediterranean and Californian summer, Australian spring, Johannesburg and Pretoria for most of the year, and any tropical beach outside the monsoon. |
| UV 9 | Very high | 19 min | 44 min | Tropical and subtropical summer, the Australian east coast from November to February, and anywhere above 1,500 m in clear summer air. |
| UV 10 | Very high | 17 min | 40 min | Northern Australia, southern Africa in December and January, the Andes and the Himalaya in summer, and the equatorial belt year-round. |
| UV 11 | Extreme | 15 min | 36 min | Equatorial noon, high-altitude tropics, and snowfields in spring — fresh snow reflects up to 80% of UV straight back at you. |
For the rest of today in Columbus
UV 1.2 right now (low) · peak UV 3.3 at 16:00 · type II has about 51 min of unprotected sun before the first redness at the peak
- 16:00 Peak UV hour
- 51 min Est. first redness at peak, type II
- Briefly Protection recommended (UV 3+, WHO)
- UV 1.2 Right now (low)
What the index does not tell you
The index is a measure of what arrives at a horizontal surface at ground level. It says nothing about what is under your feet, and that can matter as much as the sky: dry sand reflects around 15% of the UV back at you, water alongside you about 20%, fresh snow up to 80%. It also assumes sea level — every 1,000 m of altitude adds about 12%.
And it is an instantaneous reading, not a dose. Two hours at UV 4 and one hour at UV 8 deliver the same energy to your skin. The reason the second one is worse is that the erythemal threshold arrives inside that hour, and once you cross it the skin does not average anything out.
Where the sun is strongest right now
- London — UV 4.2Moderate · United Kingdom · peak at 13:00 tomorrow · type II: 40 min to first redness at the peak
- Dublin — UV 3.8Moderate · Ireland · peak at 13:00 tomorrow · type II: 44 min to first redness at the peak
- Bristol — UV 3.6Moderate · United Kingdom · peak at 12:00 tomorrow · type II: 46 min to first redness at the peak
Questions about the UV index scale
What is the UV index scale?
An open-ended scale starting at 0, where one point equals 25 milliwatts per square metre of erythemally weighted UV irradiance. The World Health Organization groups it into five bands: low (0–2), moderate (3–5), high (6–7), very high (8–10) and extreme (11+). The scale has no fixed ceiling; readings above 15 occur in the tropical Andes.
What is a high UV index?
UV 6 and 7 are the high band, 8 to 10 very high, 11 and above extreme. In practical terms: at UV 6, fair skin (type II) reaches the first redness in about 28 min; at UV 8 it is 21 min; at UV 11 it is 15 min.
Does the UV index depend on temperature?
No, and this is the single most common misreading of it. The UV index depends on the angle of the sun, the ozone column, altitude and cloud. A clear day at 8°C in the mountains carries more UV than a hazy day at 32°C at sea level. Heat is infrared; sunburn is ultraviolet.
How much does cloud reduce the UV index?
Far less than the drop in temperature suggests. Half cloud cover removes about 7% of the UV; a fully overcast sky removes about 75%. So a UV 8 day under complete cloud is still around UV 2, and a UV 8 day under scattered cloud is still essentially UV 8.