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Calculate Heat Index
Temperature: °F °C K

Relative Humidity (%):

Heat Index Units: °F °C K

Heat Index:

Key Values:

Key Values for the Heat Index

Note: Exposure to full sunshine can increase heat index values by up to 15°F.


Equations:

Note: This calculator follows the methods used by NOAA's Weather Prediction Center to calculate the heat index. This is a refinement of Rothfusz (1990, Technical Attachment SR 90-23).

Rothfusz (1990) is not appropriate for heat indices less then 80°F. The following equation is used for heat indices below 80°F:

Equation Heat Index Below 80

If the heat index is 80°F or higher, then Rothfusz (1990) is used:

Typical Heat Index Equation

If the relative humidity is less than 13% and the temperature is between 80°F and 112°F (inclusive), then an adjustment is subtracted from the Rothfusz (1990) heat index :

Heat Index Equation Adjustment 1

If the relative humidity is greater than 85% and the temperature is between 80°F and 87°F (inclusive), then an adjustment is added to the Rothfusz (1990) heat index :

Heat Index Equation Adjustment 2

In the above equations, HI is the heat index in °F, T is the temperature in °F, and RH is the relative humidity in percent.