🌡️Heat Index Calculator
Best for T > 27°C / 80°F
40–100%
The heat index (also called apparent temperature or feels-like temperature in summer) estimates how hot it actually feels based on air temperature and relative humidity. High humidity prevents sweat from evaporating effectively, reducing the body's ability to cool itself. The Rothfusz (1990) regression equation used by NOAA and the NWS is the most widely accepted formula.
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Tip: Heat index assumes shaded conditions. Direct sunlight can add an additional 8–15°C to the apparent temperature. Drink water before you feel thirsty — thirst indicates you are already mildly dehydrated.
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