UV Exposure Estimate Calculator
Estimate erythemally weighted ambient UV exposure from a UV Index and duration; not a personal skin dose or safe-time limit.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
This educational calculation converts the supplied UV Index to erythemally weighted irradiance (UVI ÷ 40) and multiplies it by exposure duration. It estimates incident ambient energy only—not absorbed skin dose, burn time or a safe exposure limit. The UV Index is a public indicator of potential harm; use current local guidance and sun-protection advice.
Worked example
calculated with the default values below
UV Index 8 · Exposure duration 10 min Erythemally weighted irradiance 0.2000 W/m² · Estimated ambient radiant exposure 120.0 J/m² · UV Index category Very high
General background references
Disclaimer
These calculators give general estimates. Sizing, pricing, availability and standards vary by brand, retailer and country, so treat the output as a starting point and confirm it against the seller's or authority's own figures.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
E_eff = UVI÷40; H = E_eff×t×60
- UVI
- UV Index
- E_eff
- Erythemally weighted ambient irradiance (W/m²)
- t
- Exposure duration (min)
- H
- Incident ambient radiant exposure (J/m²)
UVI = 40×E_eff (W/m²); H = E_eff×t×60 (J/m²). H is incident ambient erythemally weighted radiant exposure, not absorbed personal dose or a safe-time limit. See WHO UV Index guidance: https://www.who.int/news-room/fact-sheets/detail/ultraviolet-radiation.
Frequently asked questions
Does this tell me how long it is safe to stay in the sun?
No. It converts UVI to erythemally weighted ambient irradiance (UVI ÷ 40) and multiplies by minutes. The result is incident environmental energy, not a personal skin dose, burn-time prediction or safe limit. The WHO describes UVI as an indicator of potential harm; follow current local advice. [WHO UV guidance](https://www.who.int/news-room/fact-sheets/detail/ultraviolet-radiation).