Select the current UV index and your skin type (Fitzpatrick scale) to get the WHO risk level, an estimated time to sunburn with no protection, and the minimum recommended SPF.
| UV index | WHO risk level | Minimum recommended SPF |
|---|---|---|
| 0-2 | Low | SPF 15+ |
| 3-5 | Moderate | SPF 30+ |
| 6-7 | High | SPF 30 to 50 |
| 8-10 | Very High | SPF 50+ |
| 11+ | Extreme | SPF 50+ |
These are general order-of-magnitude figures for information only and do not replace dermatological advice. Actual sunburn time depends on many individual factors: exact skin type, photosensitising medication, altitude, reflection off snow, sand, or water, time of day, and cloud cover. This tool does not calculate protection time once a specific sunscreen is applied.
Understanding the WHO UV index scale
The UV index is a scale developed by the World Health Organization to describe the strength of ultraviolet radiation reaching the ground at a given place and time. It has nothing to do with air temperature: a cold, clear spring day at altitude can carry a higher UV index than a warm, hazy summer afternoon, because the index depends on the sun's angle, ozone thickness, altitude, and cloud cover rather than how hot the air feels. A UV index of 0 to 2 is Low, 3 to 5 is Moderate, 6 to 7 is High, 8 to 10 is Very High, and 11 or above is Extreme. The UK Met Office reports this figure daily alongside its weather forecasts precisely because sunburn risk depends on it far more than on temperature.
Fitzpatrick skin types and reference sunburn times
| Skin type | Reaction to sun | Reference time to sunburn at UV 10 |
|---|---|---|
| I | Very fair, always burns, never tans | About 10 minutes |
| II | Fair, usually burns, tans minimally | About 15 to 20 minutes |
| III | Medium, sometimes burns mildly, tans gradually | About 20 to 30 minutes |
| IV | Olive, rarely burns, tans easily | About 30 to 45 minutes |
| V | Brown, very rarely burns, tans darkly and easily | About 60 minutes |
| VI | Deeply pigmented, almost never burns | Over 90 minutes |
These reference times shorten roughly in proportion as the UV index rises above 10, and stretch out roughly in proportion when it drops below 10.
What this guide cannot do
The figures shown here are general dermatological reference points, not a precise calculation. Real sunburn time also changes with altitude, reflection off snow, sand, or water, time of day, cloud cover, and individual factors such as photosensitising medication or a personal history of skin cancer. This guide does not replace a dermatologist's advice. It is also deliberately different from a sunscreen protection time calculator: it only estimates how long unprotected skin takes to burn and gives a minimum recommended SPF band, it does not calculate an exact protection duration once a specific sunscreen with a given SPF has been applied, which depends on application thickness, reapplication, sweating, and swimming.
Practical recommendations by risk level
At Low risk, most people can stay outside without protection. From Moderate risk upward, the Met Office and UK dermatology bodies recommend seeking shade during the middle of the day, wearing a hat and UV-blocking sunglasses, and applying sunscreen of at least the SPF band shown above, reapplied every two hours and after swimming or sweating. At Very High and Extreme risk, unprotected skin of any type can burn within minutes at midday, so limiting direct exposure between 11am and 3pm is the most reliable precaution. For a related but different figure, the heat index calculator works out how hot the air actually feels rather than how strong the UV radiation is.