# Heat Index Calculator

> Heat index calculator: convert air temperature and humidity into the feels-like heat index and outdoor risk level. Free, private, runs in your browser.

- **Canonical URL:** https://boringtoolskit.com/heat-index-calculator/
- **Category:** Everyday Calculators
- **Evidence level:** authored-methodology
- **Reviewed:** August 2026
- **Last verified:** 2026-10-12
- **Privacy:** Inputs and results stay in this browser unless the page clearly labels an external request.

## How it works

Rothfusz regression: HI = -42.379 + 2.04901523T + 10.14333127R - 0.22475541TR - 6.83783e-3T^2 - 5.481717e-2R^2 + 1.22874e-3T^2R + 8.5282e-4TR^2 - 1.99e-6T^2R^2, T in Fahrenheit, R in %.

## Worked example

90 Fahrenheit at 60% relative humidity: a heat index of about 100 Fahrenheit.

## Sources

- [Calculation methodology and verification standard](/methodology/)

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