A heat index calculator computes the apparent temperature, or how hot the air feels to the human body, by combining actual air temperature and relative humidity.
About this calculator
A heat index calculator computes the apparent temperature, or how hot the air feels to the human body, by combining actual air temperature and relative humidity. High humidity prevents sweat from evaporating well, which makes hot days feel hotter than the air temperature alone suggests.
The heat index formula (Steadman, 1979) is used by meteorologists and health authorities when heat and humidity together pose health risks.
Common uses
- Check real feel temperature before outdoor activities
- Assess heat stroke risk for outdoor workers or athletes
- Plan hydration and rest breaks for hot weather events
- Determine when outdoor activity becomes dangerous
Frequently asked questions
At what heat index does heat stroke become a risk?
Heat index risk levels: 27–32°C (Caution), 32–41°C (Extreme Caution, heat cramps possible), 41–54°C (Danger, heat exhaustion likely), above 54°C (Extreme Danger, heat stroke highly likely). Stay hydrated, seek shade, and avoid strenuous activity during dangerous heat index levels.