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Heat Index vs. Humidity

The influence of humidity on the apparent temperature and the heat index.

The Heat Index - or the Apparent Temperature - is used to indicate how hot it feels when relative humidity is combined with temperature.

With increased humidity it feels hotter as indicated in the Heat Index table bellow:

Heat Index vs. Humidity
Heat Index
Dry Temperature
 		Relative Humidity (%)
(oF)(oC)0102030405060708090100
70 21.1 64 65 66 67 68 69 70 70 71 71 72
75 23.9 69 70 72 73 74 75 76 77 78 79 80
80 26.7 73 75 77 78 79 81 82 85 86 88 91
85 29.4 78 80 82 84 86 88 90 93 97 102 108
90 32.2 83 85 87 90 93 96 100 106 113 122  
95 35 87 90 93 96 101 107 114 124 136    
100 37.8 91 95 99 104 110 120 132 144      
105 40.6 95 100 105 113 123 135 149        
110 43.3 99 105 112 123 137 150          
115 46.1 103 111 120 135 151            
120 48.9 107 116 130 148              

Heat and Humidity Index Danger Zones

  • 90 - 104 : Heat cramps or heat exhaustion possible
  • 105 - 130 : Heat cramps or heat exhaustion likely, heatstroke possible
  • 130 and more : Heat stroke highly likely

Example - Apparent Temperature

From the table - with dry temperature 85 oF and relative humidity 80% - the apparent temperature - or Heat Index - is 97 oF.

heat and humidity index danger zones

Related Topics

  • Air Psychrometrics

    Moist and humid air calculations. Psychrometric charts and Mollier diagrams. Air-condition systems temperatures, absolute and relative humidities and moisture content in air.

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