Heat Index Calculator
Calculate apparent temperature from air temperature and humidity
About this calculator
The Heat Index Calculator determines how hot it actually feels to the human body by combining air temperature and relative humidity levels. This apparent temperature, also known as the "feels like" temperature, is crucial for understanding heat stress risks and making informed decisions about outdoor activities. High humidity prevents sweat from evaporating effectively, making the body feel hotter than the actual air temperature. This tool helps assess heat-related health risks and plan appropriate safety measures during hot, humid conditions.
How to use
Enter the current air temperature in degrees Fahrenheit or Celsius, then input the relative humidity percentage. The calculator will instantly compute the heat index, showing you the apparent temperature that accounts for both heat and moisture in the air.
Frequently asked questions
What is a dangerous heat index level?
Heat index values above 105°F (40°C) are considered dangerous, with extreme caution needed above 90°F (32°C) for prolonged exposure or physical activity.
Why does humidity make temperature feel hotter?
High humidity prevents sweat from evaporating efficiently, reducing the body's natural cooling mechanism and making the air temperature feel significantly warmer.
Is heat index the same as wind chill?
No, heat index measures how hot it feels in summer conditions, while wind chill measures how cold it feels in winter weather.