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Heat Index Chart

The Heat Index, given in degrees Fahrenheit, is an accurate measure of how hot it really feels when effects of the relative humidity (RH) is added to the actual air temperature. To determine the Heat Index, look at the Heat Index Chart below. As an example, if the air temperature is 96 degrees F (found on the left side of the table) and the RH is 55% (found at the top of the table), the HI - or how hot it really feels - is 112 degrees F. This is at the intersection of the 96 degree row and the 55% column.

Since HI values were devised for shady, light wind conditions, exposure to full sunshine can increase heat index values by up to 15° F. Also, strong winds, particularly with very hot, dry air, can be extremely hazardous. Click here for safety precautions to take during heat waves.

HEAT INDEX °F (°C)
  RELATIVE HUMIDITY (%)
Temp. 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 97 100 103 106 110 114 119 124 129 135      
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


Category Heat Index Possible heat disorders for people in high risk groups
Extreme
Danger		 130°F or higher
(54°C or higher)		 Heat stroke or sunstroke likely.
Danger 105 - 129°F
(41 - 54°C)		 Sunstroke, muscle cramps, and/or heat exhaustion likely. Heatstroke possible with prolonged exposure and/or physical activity.
Extreme
Caution		 90 - 105°F
(32 - 41°C)		 Sunstroke, muscle cramps, and/or heat exhaustion possible with prolonged exposure and/or physical activity.
Caution 80 - 90°F
(27 - 32°C)		 Fatigue possible with prolonged exposure and/or physical activity.


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Date modified:July 18, 2006		 Comments/Feedback
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