Heat Index Calculator
Apparent temperature from heat and humidity.
Enter your values
ⓘ Live results
Results
- Feels like
- 108.3 °F
- In Celsius
- 42.4 °C
- Added by humidity
- 16.3 °F
- Risk level
- Danger
- Guidance
- Limit outdoor exertion; heat illness likely
Quick answer
The heat index combines temperature and humidity using the NWS Rothfusz regression; it applies above about 80°F.
How to use the Heat Index Calculator
- 1Enter the air temperature in Fahrenheit.
- 2Enter the relative humidity.
- 3Read the feels-like temperature and risk band.
Worked example
Using the values the calculator loads with:
Inputs
- Air temperature92 °F
- Relative humidity65 %
Results
- Feels like108.3 °F
- In Celsius42.4 °C
- Added by humidity16.3 °F
- Risk levelDanger
- GuidanceLimit outdoor exertion; heat illness likely
Frequently asked questions
Why does humidity make heat worse?
Sweat cools you by evaporating. In humid air it evaporates slowly, so your body cannot shed heat.
Is heat index measured in shade?
Yes. Full sun can add up to 15°F to the values shown.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.