How do I calculate heat index? Enter your numbers above and the result updates instantly. For example: Air temperature: 92 °F · Relative humidity: 60% → Heat index: 105°F.
Is this Heat Index Calculator free? Yes — completely free with no sign-up or paywall. It runs entirely in your browser and keeps working offline; the numbers you enter never leave your device.
How accurate is it? It uses the standard published formula for heat index. Results are estimates for planning — not financial, tax, medical, engineering, or legal advice.