What is the UV index?

The UV index (UVI) is an international standard scale developed by WHO and WMO that measures the intensity of ultraviolet radiation from the sun at a specific location. A higher number means greater potential for skin and eye damage, and a shorter time to cause sunburn.

What UV index is considered dangerous?

WHO classifies UV index 3–5 as Moderate, 6–7 as High, 8–10 as Very High, and 11+ as Extreme. Values of 6 or above warrant protective measures such as sunscreen SPF 30+, protective clothing, and seeking shade during midday hours.

How are safe exposure times calculated?

Safe exposure time is estimated using the Minimal Erythemal Dose (MED) for each Fitzpatrick skin type divided by the UV index multiplied by 0.025 (the UV irradiance per index unit in W/m²). Results are approximate and assume no sunscreen protection.

What is the Fitzpatrick scale?

The Fitzpatrick scale classifies human skin color into six types (I–VI) based on its response to UV exposure. Type I (very fair) burns easily and never tans, while Type VI (very dark) burns rarely and tans very easily. Fair skin has a much shorter safe exposure window under high UV.

Does cloud cover lower the UV index?

Light cloud cover reduces UV by 10–25%, while heavy overcast can cut it by 50–75%. However, thin or broken clouds can sometimes increase UV by reflecting it. Snow, sand, and water also reflect UV and can significantly increase effective exposure.

How often should I reapply sunscreen?

Regardless of UV level, sunscreen should be reapplied every two hours and immediately after swimming or heavy sweating. On high UV days (6+), use SPF 30 or higher and combine with protective clothing and shade.

UV Index Explainer

Name: UV Index Explainer
Availability: InStock
Author: Nham Vu

Enter a UV index value to instantly see the risk level, protection advice, and safe exposure time for your skin type.

Enter UV Index

UV Index Value (0–16+)

0 Low 8 11+ Extreme

Quick Presets

Risk categories follow the WHO Global Solar UV Index standard. Exposure times shown assume no sunscreen protection.

Enter a UV index value or drag the slider
to see risk level and protection advice.

Summary

Enter a UV index value to instantly see the risk level, protection advice, and safe exposure time for your skin type.

How it works

Enter a UV index value between 0 and 16 (values above 11 are considered Extreme).
The tool maps the value to the WHO five-level risk scale: Low, Moderate, High, Very High, or Extreme.
A color-coded visual scale highlights your position on the UV spectrum.
Protection recommendations (sunscreen, clothing, shade, timing) are shown for your risk level.
Safe exposure times for six Fitzpatrick skin types are calculated and displayed in a table.
Adjust the value using the slider or type directly into the input for instant feedback.

Use cases

Check UV risk before heading outdoors for exercise, sports, or leisure.
Teach children or students about the UV index scale and sun safety.
Plan beach trips, hikes, or outdoor events based on forecasted UV levels.
Understand UV forecasts reported in weather apps and news.
Assess sunburn risk for fair-skinned or sensitive individuals.
Compare UV intensity across different seasons, altitudes, or latitudes.
Determine when reapplication of sunscreen is critical.
Guide outdoor workers on appropriate protective clothing and break schedules.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu