Weather
Heat Index Calculator
Blend air temperature with relative humidity to reveal the true feels-like temperature plus a quick risk label for outdoor work or workouts.
Blend air temperature with relative humidity to find the feels-like value.
NOAA heat index
Uses the Rothfusz/Steadman regression adopted by NOAA: a polynomial that inputs dry-bulb °F and relative humidity to output heat index in °F (converted to °C for completeness).
How to use
- Choose Fahrenheit or Celsius and enter the actual air temperature.
- Enter the relative humidity percentage from your forecast or hygrometer.
- Review the feels-like value in °F/°C plus the matching caution, extreme caution, or danger guidance.
Example
Input: Temperature = 92°F, Humidity = 70%
Output: Heat index ≈ 112°F (44°C), labeled Extreme caution
FAQ & notes
When is the heat index formula accurate?
NOAA’s regression is most reliable when temperatures are ≥ 80°F (27°C) and humidity is above ~40%. Outside that range the feels-like value equals the air temperature.
Does wind or direct sun change the result?
The published formula assumes shade with light wind. Direct sunlight or stagnant air can add several more degrees of perceived heat.