Heat Index Calculator

Estimate shade-based heat index locally with the NWS Steadman/Rothfusz method and see Celsius and Fahrenheit results.

Air temperature

Temperature unit

Relative humidity (%)

—Heat index

—Other temperature scale

—Method used

—Dew point

NWS heat index is a shade/light-wind apparent-temperature model. The full Rothfusz regression is used when the preliminary value is at least about 80°F; values outside the model's intended conditions should not be treated as an official warning product.

How to use this Heat Index Calculator

Calculate the U.S. National Weather Service heat index from air temperature and relative humidity. Enter your values above and the result is calculated directly in your browser. No account is required.

Fast answer, clear inputs

This tool is built around one job: give the answer quickly without forcing a signup or hiding the result. Related tools are linked nearby when the next calculation or conversion is useful.