Heat Index Calculator

Use this heat index calculator to estimate how hot the air may feel when humidity is added to the actual temperature. It is useful for workouts, outdoor work, travel, school schedules, events and any day when you want a quick sense of heat stress before staying outside for long.

Enter the air temperature and relative humidity. The tool converts the value into the standard formula set commonly referenced by the U.S. National Weather Service, applies the appropriate method for the range and returns an estimated apparent temperature plus a practical risk category.

Heat index is defined for shady conditions with light wind. In direct sun, the apparent temperature can feel even worse. Treat the result as a practical planning aid for hydration, breaks, clothing and exposure decisions rather than medical advice.