Heat Index Calculator

The heat index (feels-like temperature) combines air temperature and relative humidity to determine the apparent temperature. High humidity impairs the body's ability to cool itself through sweating, making hot conditions feel significantly hotter than the thermometer reads.

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1. 1Uses the Rothfusz regression equation (NWS, USA)
2. 2Only applicable when temperature > 27°C (80°F) and humidity > 40%
3. 3Below this threshold, the actual temperature is used directly
4. 4HI = −42.379 + 2.04901523T + 10.14333127RH − 0.22475541TH − 0.00683783T² − 0.05481717RH² + ...