UV Index Calculator

1. Enter the UV index for your location, from a weather app or forecast.
2. Choose the skin type that best matches how your skin reacts to sun.
3. Add a sunscreen SPF if you plan to wear one, or leave it blank.
4. Read the estimated time to sunburn and the UV risk band.

Here is what each result means:

The UV index is a simple scale that shows how strong the sun's ultraviolet radiation is at a given place and time. It runs from 0 upward, with higher numbers meaning a faster risk of skin and eye damage.

The scale was designed by the World Health Organization and is used worldwide. A UV index of 0 to 2 is low, while 11 or above is extreme. The number already accounts for the sun's angle, so it peaks around midday and in summer.

The estimate combines two ideas: how strong the UV is, and how sensitive your skin is. Stronger UV burns faster, and fairer skin burns faster than darker skin.

Here B is a base time in minutes for your skin type at a UV index of 1. That base comes from published minimal erythemal dose values, the standard measure of how much UV each skin type can take before it reddens. Dividing by the UV index scales the time to today's conditions.

1. Look up the base minutes for your skin type.
2. Divide by the UV index to get the unprotected burn time.
3. Multiply by the SPF, if entered, to estimate the protected time.

Real sunscreen protection is usually lower than the lab SPF, because most people apply too little and rub some off. Treat the protected time as a best case, and always reapply.

Take a bright summer day with a UV index of 9 and Type II skin, which usually burns and tans a little.

Calculation: the base time for Type II skin is about 167 minutes at a UV index of 1. Dividing by 9 gives roughly 19 minutes of unprotected time before skin may start to burn. With SPF 30 applied well, that best-case time stretches to several hours, but you should still reapply every 2 hours.

The US Environmental Protection Agency groups UV index values into five risk bands, each with recommended protection.

The Fitzpatrick scale sorts skin into six types by how it reacts to sun. Fairer types burn faster and need more protection.

All skin types can suffer UV damage, including skin cancer, even those that rarely burn. Darker skin has more natural protection, but it is not immune.

Use Sunscreen Correctly

Choose a broad-spectrum sunscreen of SPF 30 or higher. Apply it generously about 15 minutes before going out, and reapply every 2 hours, and after swimming or sweating.

Seek Shade at Midday

UV is strongest from about 10am to 4pm. Staying in shade during those hours cuts your exposure sharply, whatever your skin type.

Cover Up

A wide-brimmed hat, sunglasses, and light long-sleeved clothing block UV that sunscreen can miss. Clothing is often the most reliable protection.

1. Trusting the SPF Time as a Guarantee

The protected time is a best case with perfect application. Most people apply too little, so real protection is lower. Reapply every 2 hours no matter what.

2. Assuming Clouds Block UV

Up to 80 percent of UV passes through light cloud. You can burn on an overcast day, so check the UV index, not just the brightness.

3. Ignoring Reflection

Water, sand, and snow bounce UV back onto your skin, raising your exposure. Snow can nearly double it, which is why sunburn happens while skiing.

4. Thinking Darker Skin Cannot Burn

Darker skin burns more slowly but is not immune. Every skin type faces UV damage and needs some protection under strong sun.

This tool gives a general estimate from published reference values. It cannot predict any individual's exact burn time, which depends on many personal factors.

Sun sensitivity varies widely between people. When in doubt, protect earlier and reapply more often than any estimate suggests.

It depends on the UV index and your skin type. At a UV index of 9, fair Type II skin can start to burn in about 20 minutes unprotected, while darker skin takes longer. This is a general estimate, not a guarantee.

The UV index is a World Health Organization scale showing how strong the sun's ultraviolet radiation is. It runs from 0 upward, with 0 to 2 low and 11 or more extreme. Higher numbers mean skin burns faster.

In theory, SPF 30 lets skin take about 30 times more sun before burning. In practice, protection is lower because most people apply too little sunscreen, so you should reapply at least every 2 hours regardless.

Pick the Fitzpatrick description that matches how your skin reacts to sun. Skin that always burns and never tans is Type I, while skin that never burns and is deeply pigmented is Type VI.

Yes. Up to 80 percent of UV passes through light cloud, so you can burn even when the sky looks overcast. Check the UV index rather than relying on how bright it seems.

Yes. Water, sand, and especially snow reflect UV back onto your skin, raising your total exposure. Snow can nearly double it, so burns happen quickly while skiing or on the beach.

Yes. Darker skin has more natural protection and burns more slowly, but it is not immune. Every skin type can suffer UV damage, including skin cancer, and needs some protection under strong sun.

No. The calculation runs in your browser and nothing you enter is stored or sent anywhere, unless you choose Save, which keeps the result only on this device.

• Global Solar UV Index: A Practical Guide (World Health Organization).
• UV Index Scale (US Environmental Protection Agency).