Heat index calculator
Find the heat index, or 'feels like' temperature, from the air temperature and relative humidity.
About this calculator
Enter the air temperature and humidity. The calculator uses the US National Weather Service regression to give the temperature it feels like, with a risk level.
It is meant for shade and light wind. Direct sunlight can make it feel up to 8 °C (15 °F) hotter.
Measurements and terms explained
- Heat index
- The apparent temperature that combines air temperature and humidity.
- Relative humidity
- How much water vapour the air holds as a percentage of the most it could hold at that temperature.
Common questions
Why does humidity make it feel hotter?
Sweat evaporates more slowly in humid air, so your body cools less well.
When is the heat index used?
Mostly when air temperature is above about 27 °C (80 °F) with moderate or high humidity.
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