Heat Index Calculator
Calculate how hot it really feels using temperature and humidity.
Weather Conditions
What is the Heat Index Calculator?
The Heat Index Calculator determines the "feels like" temperature during summer months. Because high humidity prevents sweat from evaporating off human skin, the body cannot cool itself properly, making a humid 90°F day feel dangerously hotter than a dry 90°F day.
How It Works (Formula)
The tool uses the complex polynomial equation utilized by the National Oceanic and Atmospheric Administration (NOAA). It mathematically combines ambient air temperature with relative humidity to find the perceived temperature.
$$ \text{HI} = c_1 + c_2T + c_3R + c_4TR - c_5T^2 - c_6R^2 \dots $$
A multi-variable regression equation used by meteorologists.
How to Use It
Enter the current air temperature (must be 80°F or higher for the equation to work) and the current relative humidity percentage. The calculator will immediately output the Heat Index and warn you of potential heat stroke danger zones.