Heat Index Chart and Heat Index Calculator
 
What is Heat Index?
  Heat Index
Heat index is a mathematical formula that combines air temperature and relative humidity to calculate an apparent temperature how hot it feels. The human body normally cools itself by sweating, as the water in sweat evaporates and carries heat away from the body. But when relative humidity is high, water doesn't evaporate as quickly, so the body retains more heat.
 
 
Heat Index Charts
  Relative Humidity (%)
40 45 50 55 60 65 70 75 80 85 90 95 100
110 136 - - - - - - - - - - - -
108 130 137 - - - - - - - - - - -
106 124 130 137 - - - - - - - - - -
104 119 124 131 137 - - - - - - - - -
102 114 119 124 130 137 - - - - - - - -
100 109 114 118 124 129 136 - - - - - - -
98 105 109 113 117 123 128 134 - - - - - -
96 101 104 108 112 116 121 126 132 - - - - -
94 97 100 102 106 110 114 119 124 129 135 - - -
92 94 96 99 101 105 108 112 116 121 126 131 - -
90 91 93 95 97 100 103 106 109 113 117 122 127 132
88 88 89 91 93 95 98 100 103 106 110 113 117 121
86 85 87 88 89 91 93 95 97 100 102 105 108 112
84 83 84 85 86 88 89 90 92 94 96 98 100 103
82 81 82 83 84 84 85 86 88 89 90 91 93 95
80 80 80 81 81 82 82 83 84 84 85 86 86 87

With Prolonged Exposure and/or Physical Activity:
Caution:
Fatigue possible
Extreme Caution:
Sunstroke, muscle cramps, and/or heat exhaustion possible
Danger:
Sunstroke, muscle cramps, and/or heat exhaustion likely
Extreme Danger:
Heat Stroke or Sunstroke likely

Heat Index Calculator

Valid entries are, air temperatures greater than 80 F ( 27 C ), dew point temperatures greater than 60 F ( 16 C ), and relative humidities higher than 40 percent.

in Fahrenheit

Enter in the air temperature ( Tair ) in degrees Fahrenheit and relative humidity ( RH ) in percent ( without the % sign ), then click on Calculate to compute the heat index ( HI ).
Tair in °F RH Tdp =
in Celsius

Enter in the air temperature ( Tair ) in degrees Celsius and relative humidity ( RH ) in percent ( without the % sign ), then click on Calculate to compute the heat index ( HI ).
Tair in °C RH Tdp =

Heat Index Calculator

Valid entries are, air temperatures greater than 80 F ( 27 C ), dew point temperatures greater than 60 F ( 16 C ), and relative humidities higher than 40 percent.

in Fahrenheit

Enter in the air temperature ( Tair ) and the dew point temperature ( Tdp ) in degrees Fahrenheit, then click on Calculate to compute the heat index ( HI).
Tair in °F Tdp in °F RH =
in Celsius

Enter in the air temperature ( Tair ) and the dew point temperature ( Tdp ) in degrees Celsius, then click on Calculate to compute the heat index ( HI).
Tair in °C Tdp in °C RH =
Heat Index Calculator Compliments of National Weather Service
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