Weather
Heat Index Calculator
Heat index from air temperature and relative humidity (°C or °F).
Free to use — no sign-up or login.
Heat index
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This free Heat Index Calculator covers Heat index from air temperature and relative humidity (°C or °F).
Heat index estimates perceived temperature in warm, humid conditions. Related weather tools sit beside How it works, with no account required.
Using the Heat Index Calculator
Heat index from air temperature and relative humidity (°C or °F). Typical inputs are Temperature unit, Temperature (°F) and Relative humidity (%). How it works beside the form states the identity the Heat Index Calculator applies.
FAQ
How do I use the Heat Index Calculator?
Open the Heat Index Calculator, fill Temperature unit, Temperature (°F) and Relative humidity (%), and read the result. Enter air temperature and relative humidity in °C or °F. Values are converted to °F for the NWS/Rothfusz regression, which estimates how hot it feels when humidity slows evaporative cooling. The result is converted back to your chosen unit.
What formula does the Heat Index Calculator use?
The Heat Index Calculator uses the identity in How it works. In words: Enter air temperature and relative humidity in °C or °F. Values are converted to °F for the NWS/Rothfusz regression, which estimates how hot it feels when humidity slows evaporative cooling. The result is converted back to your chosen unit.