How to use the Heat Index Calculator
The heat index calculator shows how hot it feels when humidity is combined with temperature.
Open the Heat Index Calculator →
What you need to enter
- Air temperature (°F)
- Relative humidity (%)
The formula
It uses the Rothfusz regression equation for temperature and relative humidity.
Worked example
Using the default values in the calculator:
- Air temperature (°F): 90
- Relative humidity (%): 60
| Heat index | 99.7 °F |
| In Celsius | 37.6 °C |
| Risk | Extreme caution |
Tips for better results
- Take care above 90 °F heat index.
- Drink water and rest.
Common mistakes to avoid
- Using it in cool weather.
- Ignoring direct sun.
Please note: Results are estimates for general use. For safety-critical work such as electrical or building projects, check with a qualified professional and local codes. See our Disclaimer.