UV Index Calculator

Enter your UV index, skin phototype, altitude, and SPF to calculate your safe sun exposure time and understand your sunburn risk. The calculator returns your maximum safe minutes in the sun, a UV risk level, and recommended sun protection actions — all based on WHO guidelines.

Enter the current UV index for your location (0 = no UV, 11+ = extreme). Check your local weather app or weather service.

Choose the general sunlight condition for your current environment.

UV intensity increases by about 10% per 1,000 m of altitude.

Snow and sand reflect up to 85–90% of UV rays, increasing your exposure.

Your skin type determines how quickly UV radiation causes damage. Type I is most vulnerable, Type V is most resistant.

Enter the SPF of your sunscreen. Use 1 if applying no sunscreen.

Results

Safe Sun Exposure Time

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UV Risk Level

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Effective UV Index

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Minimum Recommended SPF

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Safe Exposure Time by SPF Level

Results Table

Frequently Asked Questions

What is the UV Index and what does it measure?

The UV Index is an international standard measurement of the strength of ultraviolet radiation from the sun at a particular place and time. It ranges from 0 (no UV) to 11+ (extreme). The higher the UV Index, the stronger the sun's rays and the greater the risk of skin and eye damage — meaning you need stronger sun protection and shorter exposure times.

What is considered a high UV Index?

A UV Index of 6–7 is classified as High, 8–10 as Very High, and 11+ as Extreme. At these levels, unprotected skin can burn in as little as 10–15 minutes. You should apply SPF 30+ sunscreen, wear protective clothing, and seek shade especially between 10 a.m. and 4 p.m. when UV radiation peaks.

What UV index can you safely tan in?

A UV Index of 3–5 (Moderate) is generally considered the safest range for tanning, as you can still build a tan while minimising burn risk with appropriate sunscreen. Tanning at UV Index 6 or above significantly increases your skin cancer and premature ageing risk. Any tan is a sign of UV damage, so always use sunscreen regardless.

Can I still get sunburnt on a cloudy day?

Yes — clouds block only about 20–40% of UV rays, so even on overcast days you can receive a significant dose of UV radiation. Light cloud cover offers very little UV protection. It's important to check the UV Index forecast rather than relying on visible sunlight as your guide.

How does altitude affect the UV Index?

UV radiation increases by approximately 10% for every 1,000 metres (3,280 feet) of altitude gained. At high altitudes there is less atmosphere to absorb UV rays, and snow reflection compounds the effect further. Skiers and hikers at altitude need higher SPF and more frequent reapplication.

How do I calculate safe time in the sun?

The standard formula is: Safe Time (minutes) = (Skin Type Factor × SPF) ÷ (UV Index × Altitude Factor × Reflection Factor). Skin Type I has the lowest factor (around 67 minutes baseline at UV 1 with no SPF), while Type V has the highest (around 200 minutes). This calculator handles all those variables automatically.

Why are UV rays dangerous?

UV rays damage DNA in skin cells, which can lead to sunburn, premature skin ageing, and skin cancer — including melanoma, the most deadly form. UV rays also damage eyes, contributing to cataracts. The World Health Organization estimates that 80% of lifetime UV exposure occurs before age 18, making early protection habits especially important.

What SPF should I use for a given UV Index?

As a general guide: UV Index 1–2 use SPF 15+, UV Index 3–5 use SPF 30+, UV Index 6–7 use SPF 30–50+, UV Index 8–10 use SPF 50+, and UV Index 11+ use SPF 50+ with maximum clothing protection and shade. Always reapply every 2 hours and after swimming or sweating.

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