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Heat Index Calculator Step By Step
Heat Index Calculator runs in three steps: open the tool, enter temperature and humidity, then read the heat index and its risk category. This page walks through what each step expects.
Step 1 - open the tool
Go to Heat Index Calculator. Nothing needs to be installed or signed in before you start.
Step 2 - enter temperature and humidity
Pick Fahrenheit or Celsius, type the air temperature, then type the relative humidity percentage. The heat index and its NWS risk category update as soon as you change either value.
Step 3 - read the result
The apparent (feels-like) temperature appears above the risk-category name (Caution, Extreme Caution, Danger, or Extreme Danger); the reference table below the calculator explains what each category means.
The calculation runs locally in the browser - no upload and no account.
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