Created By : Naaz Fatima

Reviewed By : Rajashekhar Valipishetty

Last Updated : Apr 10, 2023

Heat Index Calculator is a handy tool that computes the heat index value given the other input parameters such as temperature, relative humidity, dew point, etc. The tool is quite flexible to use and gives you the required heat index in a matter of seconds.

Choose a Calculation
Relative Humidity:

What is Heat Index?

Heat Index or Humidex is the air temperature you feel. It considers both the air temperature and the humidity to tell how hot it feels. In general, moist air feels hotter and it is due to the evaporation of our sweat. However, heat index in shaded areas is is calculated considering the relative humidity alone. Thus, the true heat index is higher when compared to the one specified as in our tool.

Heat Index Formula

Heat Index Formula depends on two major factors i.e. relative humidity and air temperature and the rest are all constants. It involves a lot of calculations to determine the heat index manually. In that case, you can go with our Heat Index Calculator nd find it quite simply. The Formula to calculate Heat Index is given by the equation as follows


Heat Index (HI) = c1 + c2T + c3R + c4TR + c5T² + c6R² + c7T²R + c8TR² + c9T²R²


  • Where, HI is the Heat Index
  • T is the ambient Temperature in Fahrenheit
  • R is the Relative Humidity
  • c1 – c9 are constants


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Heat Index Chart

Heat Index was invented by R.G Steadman and he took almost 20 factors into consideration. You can use the Heat index Chart below for reference and make you estimations to know how high the temperature is outside. Heat Index Chart available is accurate enough and lets you know about the bad weather conditions such as heatstroke causing temperatures, etc.

Heat Index Chart in ┬░F

How to Calculate Heat Index?

Follow the simple guidelines over here and calculate the Heat Index easily. They are as follows     

  • Firstly, find out the temperature outside initially.  
  • Then, find out the relative humidity, due point, etc.
  • Later, use these input values and substitute them in the formula of heat index.
  • Simplify the equation further and get the heat index value easily.

Frequently Asked Questions on Heat Index Calculator

1. What is Heat Index?


Heat Index is a thermodynamic value that relates both air temperature and relative humidity.


2. What is the Heat Index Formula?


Heat Index Formula is given by the equation Heat Index (HI) = c1 + c2T + c3R + c4TR + c5T² + c6R² + c7T²R + c8TR² + c9T²R²


3. What is Heat Index Value?


Heat Index is a calculated temperature value that tells you how hot it feels as per the air temperature and amount of moisture in air.


4. Is the Heat Index Accurate?


Heat Index is accurate enough that you can predict the bad weather conditions so that you will be protected from heatstroke.