UV index burn time calculator
Choose the UV index and your skin type to see roughly how long unprotected skin takes to start reddening. Read the result as a warning, not an allowance: UV harms skin before redness shows, and WHO advises protection from UV 3 upward.
Unprotected skin can start to redden in
about 20 minutes
High · 6–7 Cut midday sun; shade, clothing, hat, sunglasses and sunscreen.
A warning, not a safe time. Redness shows up hours later.
Minutes to first redness at every UV index
| UV index | Type I | Type II | Type III | Type IV | Type V | Type VI |
|---|---|---|---|---|---|---|
| 1 | 100 | >120 | >120 | >120 | >120 | >120 |
| 2 | 50 | 65 | 100 | >120 | >120 | >120 |
| 3 | 35 | 45 | 65 | 100 | >120 | >120 |
| 4 | 25 | 35 | 50 | 75 | 100 | >120 |
| 5 | 20 | 25 | 40 | 60 | 80 | >120 |
| 6 | 15 | 20 | 35 | 50 | 65 | 110 |
| 7 | 15 | 20 | 30 | 45 | 55 | 95 |
| 8 | 15 | 15 | 25 | 40 | 50 | 85 |
| 9 | 10 | 15 | 20 | 35 | 45 | 75 |
| 10 | 10 | 15 | 20 | 30 | 40 | 65 |
| 11+ | <10 | 10 | 20 | 25 | 35 | 60 |
How to use the calculator
- Check today's highest UV index in a weather app or with your national weather service.
- Select that value, from 1 to 11+.
- Choose the skin type that matches how your skin reacts to the first strong sun of summer.
- Protect yourself well before the time shown, especially from UV 3 upward.
Why the result ignores sunscreen
The calculator never adds time for sunscreen, on purpose. Most people apply far less than the amount used to test SPF, so they get perhaps a fifth to a half of the protection on the label. Sweat, water and towels remove it, and it needs reapplying at least every two hours. WHO is clear: sunscreen is extra protection for skin you cannot cover, not a way to stay in the sun longer.
What changes the real time
- Fresh snow reflects up to about 80% of UV, and sand, sea foam and water add more, so real exposure can be far higher.
- UV rises by about 10% for every 1,000 metres of altitude, so mountains burn faster than a nearby lowland forecast suggests.
- You cannot feel UV, and light cloud lets most of it through. A cool, windy or cloudy day can still burn you.
- Some medicines, including certain antibiotics, diuretics and painkillers, and some perfumes and plant juices make skin burn much faster. Ask your pharmacist.
- Children need extra care: WHO says babies under one year should never be in direct sun. Do not use these numbers for children.
- The UV index changes through the day and peaks around solar noon, and skin varies a lot even within one skin type.
The five UV index levels
- Low · 1–2
- WHO says the risk of UV damage at this level is limited, even for very fair skin, and under normal conditions you need no special protection. Watch for exceptions: fresh snow, water and high altitude add a lot of UV, and some medicines make skin far more sensitive. In those situations, cover up and wear sunglasses.
- Moderate · 3–5
- From UV 3 upward, WHO says protection is needed. Seek shade during the midday hours, wear a shirt, a broad-brimmed hat and sunglasses, and apply broad-spectrum sunscreen of at least SPF 15 to skin you cannot cover. Use these measures together. Unprotected fair skin can start to redden in 20 to 45 minutes.
- High · 6–7
- Protection is needed, and more of it than at moderate levels. Stay in the shade during the hours around midday, wear clothing that covers your arms and shoulders, a broad-brimmed hat and wrap-around sunglasses, and use broad-spectrum sunscreen on the skin you cannot cover. Unprotected fair skin can start to redden in about 15 to 20 minutes.
- Very high · 8–10
- WHO calls for extra protection. Avoid being outside during the midday hours where you can, and make sure you have shade when you are. A shirt, a broad-brimmed hat and sunscreen are a must, together with sunglasses. Unprotected fair skin can start to redden in about 10 to 15 minutes, and reflected UV can harm your eyes.
- Extreme · 11+
- This is the highest WHO category. Avoid the midday sun, stay in the shade, and wear a shirt, a broad-brimmed hat, wrap-around sunglasses and sunscreen on any skin left uncovered. Unprotected fair skin can start to redden in under 10 minutes, and olive skin in under half an hour. Keep babies out of direct sun and take special care with children.
Look up a UV index
How the estimate works
WHO defines one UV index unit as 25 milliwatts per square metre of sunburn-weighted UV. So every minute at UV index X gives your skin a dose of 1.5 × X joules per square metre. Sunburn doses are measured in standard erythema doses (SED); one SED is 100 joules per square metre. The dose that just reddens skin rises with skin type. We use the low end of the published range for each type, from 1.5 SED for type I to 10 SED for type VI, and divide it by the dose per minute. The redness itself appears hours later.
What UV index is safe for tanning?
Frequently asked questions
How long does it take to burn at UV 6?
Without protection at UV 6, our estimates are about 15 minutes for type I skin, about 20 for type II, roughly half an hour for type III and about 50 minutes for type IV. Snow, water or altitude make it shorter, and redness shows only hours later.
Can you tan at UV 3?
Yes, skin that tans can darken at UV 3, but WHO says protection is needed from this level up. Very fair skin can start to redden in about half an hour. A tan is your skin's response to damage, not a sign of health.
Is UV 8 dangerous?
It can be. UV 8 is in WHO's very high category. WHO advises avoiding the midday sun and says a shirt, hat and sunscreen are a must, along with shade and sunglasses. Unprotected fair skin can start to redden in 10 to 15 minutes.
Is the burn time a safe time to stay in the sun?
No. WHO warns that burn times are easily misread as a safe amount of unprotected sun. UV damages skin cells before any redness shows, and the damage adds up over your life. Treat the number as a warning and protect yourself from UV 3 upward.
Why does sunburn show up hours later?
Redness from UV is delayed. It usually starts a few hours after exposure and is strongest about 8 to 12 hours later. By the time you notice it, the dose has already been received, so do not wait for pink skin before you cover up.
Does a tan protect you from sunburn?
Only a little. WHO says a dark tan on white skin gives protection roughly equal to SPF 4, far less than you need on a sunny day. A tan is your skin's defence against damage that has already happened, so it is no reason to stay out longer.
Sources
- WHO, WMO, UNEP, ICNIRP (2002): Global Solar UV Index – A Practical Guide
- WHO (2022): Radiation – The ultraviolet (UV) index, questions and answers
- ICNIRP with ILO and WHO (2007): Protecting Workers from Ultraviolet Radiation (skin types and SED, Table 1)
- Journal of Cosmetic Dermatology: Fitzpatrick skin phototypes with typical minimal erythema dose (Table 1, after Fitzpatrick 1988 and Pathak 1987)
- CIE: Standard Erythema Dose, a Review (1 SED = 100 J/m²)