Heat index calculator

How hot humid air actually feels — the NWS Rothfusz regression on temperature and relative humidity.

US NWS Rothfusz regression with humidity adjustments. Valid from 80 °F up; below that the index equals the air temperature.

Everything runs in this browser.

How to use

  1. Enter the air temperature (°F or °C).
  2. Enter the relative humidity.
  3. Read the heat index and its danger band.

What it supports

60–140 °F and 0–100 % RH; the regression applies from 80 °F — below that a simple average with the dew point is used. Shade and calm wind are assumed; direct sun can add up to 15 °F.

Related tools

Related guides