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Calculation Machine

Heat Index Calculator

Apparent temperature from heat and humidity.

Reviewed by the Calculation Machine team · How we check our maths

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.

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Air temperature92 °F
  • Relative humidity65 %

Result

  • Feels like108.3 °F
  • In Celsius42.4 °C
  • Added by humidity16.3 °F
  • Risk levelDanger
  • GuidanceLimit outdoor exertion; heat illness likely

How to use the Heat Index Calculator

  1. 1Enter the air temperature in Fahrenheit.
  2. 2Enter the relative humidity.
  3. 3Read the feels-like temperature and risk band.

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