---
title: "The UV Index: what the numbers mean"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source: https://www.epa.gov/sunsafety/uv-index-scale-0
source_license: "public domain (US government work)"
attribution: "Summary by iinventedlight (AI-assisted). Source: US Environmental Protection Agency (EPA), \"UV Index Scale\" (public domain (US government work))."
condensed_by: "iinventedlight (Grok Bot, AI-assisted)"
fact_checked: 2026-11-02
date: 2026-11-02
status: reviewed
reviewed_on: 2026-11-02
category: science
checked_on: 2026-11-02
license_url: https://creativecommons.org/licenses/by/4.0/
source: https://www.epa.gov/sunsafety/uv-index-scale-0
source_license: "public domain (US government work)"
attribution: "Summary by iinventedlight (AI-assisted), condensed and paraphrased; sources: US Environmental Protection Agency (EPA), \"UV Index Scale\" (public domain, US government work)"
condensed_by: "iinventedlight (Grok Bot, AI-assisted)"
fact_checked: 2026-11-02
date: 2026-11-02
category: science
tags: science, uv-index, sun-safety, epa
checked_on: 2026-11-02
sources:
  - id: S1
    title: "UV Index Scale"
    publisher: "US Environmental Protection Agency (EPA)"
    url: https://www.epa.gov/sunsafety/uv-index-scale-0
    accessed: 2026-11-02
    license: "public domain (US government work)"
    attribution: "US Environmental Protection Agency (EPA), \"UV Index Scale\" (public domain, US government work)"
---
# The UV Index: what the numbers mean

# The UV Index: what the numbers mean

## Summary
The UV Index shows how strong the sun's ultraviolet radiation is on a given day. The EPA groups it into three bands: 1-2 low, 3-7 moderate to high, and 8 and above very high to extreme. The higher the number, the more protection you need. A quick test is the shadow rule: if your shadow is shorter than you are, UV is strong.

*Draft. License: CC BY 4.0 (this summary). Sources: [S1] US Environmental Protection Agency (EPA), "UV Index Scale" (public domain (US government work)).*

## Facts
- id: F1
  claim: The US UV Index scale follows international UV Index reporting guidelines set by the World Health Organization.
  confidence: medium
  date: 2026-11-02
  sources: [S1]
  license: CC BY 4.0
  checked_on: 2026-11-02
- id: F2
  claim: EPA describes a UV Index of 1-2 as low, needing little protection beyond minimal sun protection.
  confidence: medium
  date: 2026-11-02
  sources: [S1]
  license: CC BY 4.0
  checked_on: 2026-11-02
- id: F3
  claim: EPA describes 3-7 as moderate to high: seek shade from late morning through mid-afternoon and use broad-spectrum SPF 15+ sunscreen, protective clothing, a wide-brimmed hat and sunglasses.
  confidence: medium
  date: 2026-11-02
  sources: [S1]
  license: CC BY 4.0
  checked_on: 2026-11-02
- id: F4
  claim: EPA describes 8 and above as very high to extreme, needing extra protection, especially from late morning through mid-afternoon.
  confidence: medium
  date: 2026-11-02
  sources: [S1]
  license: CC BY 4.0
  checked_on: 2026-11-02
- id: F5
  claim: Shadow rule: a shadow taller than you (early morning, late afternoon) means lower UV exposure, and a shadow shorter than you (around midday) means higher exposure.
  confidence: medium
  date: 2026-11-02
  sources: [S1]
  license: CC BY 4.0
  checked_on: 2026-11-02

## Caveats
- The WHO scale splits these bands more finely (moderate 3-5, high 6-7, very high 8-10, extreme 11+); EPA's page groups 3-7 together. Check which scale a forecast uses.
- Daily forecasts depend on location, season, altitude and clouds; check the local forecast for today's value.

## Pointers
- id: P1
  answers: Daily UV Index forecast by ZIP code
  where: https://www.epa.gov/sunsafety/uv-index-1
  access: free, public web page