Enter the current temperature and relative humidity into the calculator to determine the heat index.

Heat Index Formula

The following formula is used to calculate a heat index.

HI = .5 * [ T + 61.0 + [(T-68)*.12] + (RH*.094)]

Heat Index Definition

A heat index is defined as the temperature that a person feels due to the temperature and relative humidity of the air around them.

Heat Index Example

How to calculate heat index?

  1. First, determine the relative humidity.

    Using the calculator linked above, determine the relative humidity.

  2. Next, determine the current temperature.

    Measure the temperature using an accurate thermometer.

  3. Finally, calculate the heat index.

    Using the HI formula, determine the heat index using the information from steps 1 and 2.


What is a heat index?

A heat index is the temperature that it “feels” like when taking into account relative humidity. Since human bodies use perspiration to cool off, the higher the humidity the hotter it feels like since that makes it harder to cool off.

heat index calculator
heat index formula