Calculators
Heat Index Calculator
Calculate the heat index (feels-like).
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About the Heat Index Calculator
High humidity makes heat more dangerous because sweat can't evaporate. Enter the air temperature (°F) and relative humidity and the calculator returns the heat index using the NWS Rothfusz formula. It's a key safety measure on hot, muggy days.
How to use the Heat Index Calculator
- 01Enter your air temperature and relative humidity.
- 02Read the result instantly — it recalculates as you type.
- 03Adjust the numbers to model different scenarios.
Frequently asked questions
What is the heat index?
The 'feels-like' temperature that combines air temperature and humidity. It's meaningful above about 80°F.
Why is humidity dangerous in heat?
It slows sweat evaporation, your body's main cooling method — so high humidity raises heat-illness risk sharply.