Heat Index Calculator
Calculate the 'feels like' temperature from air temperature and humidity.
Know when heat is dangerous.
Heat Index
Heat index combines air temperature and relative humidity to show how hot it actually feels.
High humidity prevents sweat from evaporating, making you feel hotter than the actual temperature.
Heat Index Danger Levels:
| Heat Index | Risk Level | Precaution |
|---|---|---|
| Below 80°F (27°C) | Comfortable | Normal activity |
| 80–90°F (27–32°C) | Caution | Fatigue possible with prolonged exposure |
| 90–103°F (32–39°C) | Extreme Caution | Heat cramps and exhaustion possible |
| 103–124°F (39–51°C) | Danger | Heat cramps and heat stroke likely |
| 125°F+ (52°C+) | Extreme Danger | Heat stroke highly likely |
The calculator uses the Rothfusz regression equation from the US National Weather Service. Both Fahrenheit and Celsius are supported.