Understanding your calculation
Method, example and limitations
How the calculation works
Heat index combines temperature and relative humidity to estimate how hot conditions can feel. The usual reference assumes shaded conditions and light wind.
Example to check
At the same hot air temperature, higher relative humidity generally raises the heat-index estimate because evaporation becomes less effective.
Before using the result
The calculation has an intended temperature and humidity range. Sun exposure, exertion, clothing and health can increase risk beyond the displayed estimate.