This calculator estimates heat index temperature felt by the human body based on the actual measured air temperature together with humidity level.

Enter the air temperature in any field, either degrees Celsius (°C) or degrees Fahrenheit (°F).
  Air Temperature
°F °C
Relative Humidity

Heat Index = °F °C

Interpret results

Risk Level


The Heat Index (HI) is a measure that combines air temperature and humidity to estimate the human-perceived temperature. It reflects the perceived warmth due to the humidity level, which affects the evaporation of sweat and cooling of the body.


The formula is given by the following equation developed by the National Weather Service (NWS):



  • 𝐻𝐼 is the Heat Index (in degrees Fahrenheit),
  • 𝑇 is the air temperature (in degrees Fahrenheit), and
  • 𝑅 is the relative humidity (percentage).

This formula is considered accurate for temperatures above 80°F (approximately 27°C) and relative humidity above 40%.


-National Weather Service (NWS), What is the heat index?


National Weather Service (NWS)

The National Weather Service is an agency of the United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weather-related products to organizations and the public for the purposes of protection, safety, and general information. Founded: February 9, 1870.