The Heat Index Calculator finds how hot it feels from air temperature and relative humidity (or dew point), using the U.S. National Weather Service equation.
Heat index: 92.7 °F = 33.7 °C
| Heat index (feels like) | 92.7 °F = 33.7 °C |
| Risk | Extreme caution: heat cramps and exhaustion possible |
| Heat index | 89.5 °F = 32.0 °C |
| Relative humidity | 60.9% |
| Risk | Caution: fatigue possible with prolonged exposure |
The heat index, or "feels like" temperature, combines air temperature and humidity. In humid air, sweat evaporates more slowly, so the body cools less effectively and feels hotter. It is calculated for shade; direct sunlight can add up to 15 °F.
The National Weather Service uses the Rothfusz regression, a formula fitted to Steadman's apparent temperature tables, with adjustments for very low or high humidity.
Worked example (defaults): 85 °F at 70% humidity feels like about 93 °F (34 °C), in the "extreme caution" range.
80–90 °F: fatigue with long exposure. 90–103 °F: heat cramps and exhaustion possible. 103–124 °F: heat exhaustion likely, heat stroke possible. 125 °F+: heat stroke highly likely. Drink water, rest in shade or air conditioning, and check on vulnerable people.
What are signs of heat stroke? Confusion, hot dry skin, high body temperature; call emergency services.
Why is humidity so important? It limits evaporation of sweat.
Is heat index the same as WBGT? No, WBGT also accounts for sun and wind.