Calculator for Heat Index from Temperature and Relative Humidity

Yeah... so maybe it reads 90° on the thermometer... but at 87% relative humidity it FEELS LIKE it is 119° instead. The heat index (HI) is a measure of how hot it feels when relative humidity (RH) is added to the actual air temperature. Try it!

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) and the dewpoint (Tdp). Valid entries are air temperatures greater than 80 °F, and relative humidities higher than 40 percent.

Tair in °F RH Tdp =

HEAT INDEX °F (°C)
  RELATIVE HUMIDITY (%)
Temp. 40 45 50 55 60 65 70 75 80 85 90 95 100
110
(47)		 136
(58)		                        
108
(43)		 130
(54)		 137
(58)		                      
106
(41)		 124
(51)		 130
(54)		 137
(58)		                    
104
(40)		 119
(48)		 124
(51)		 131
(55)		 137
(58)		                  
102
(39)		 114
(46)		 119
(48)		 124
(51)		 130
(54)		 137
(58)		                
100
(38)		 109
(43)		 114
(46)		 118
(48)		 124
(51)		 129
(54)		 136
(58)		              
98
(37)		 105
(41)		 109
(43)		 113
(45)		 117
(47)		 123
(51)		 128
(53)		 134
(57)		            
96
(36)		 101
(38)		 104
(40)		 108
(42)		 112
(44)		 116
(47)		 121
(49)		 126
(52)		 132
(56)		          
94
(34)		 97
(36)		 100
(38)		 103
(39)		 106
(41)		 110
(43)		 114
(46)		 119
(48)		 124
(51)		 129
(54)		 135
(57)		      
92
(33)		 94
(34)		 96
(36)		 99
(37)		 101
(38)		 105
(41)		 108
(42)		 112
(44)		 116
(47)		 121
(49)		 126
(52)		 131
(55)		    
90
(32)		 91
(33)		 93
(34)		 95
(35)		 97
(36)		 100
(38)		 103
(39)		 106
(41)		 109
(43)		 113
(45)		 117
(47)		 122
(50)		 127
(53)		 132
(56)
88
(31)		 88
(31)		 89
(32)		 91
(33)		 93
(34)		 95
(35)		 98
(37)		 100
(38)		 103
(39)		 106
(41)		 110
(43)		 113
(45)		 117
(47)		 121
(49)
86
(30)		 85
(29)		 87
(31)		 88
(31)		 89
(32)		 91
(33)		 93
(34)		 95
(35)		 97
(36)		 100
(38)		 102
(39)		 105
(41)		 108
(42)		 112
(44)
84
(29)		 83
(28)		 84
(29)		 85
(29)		 86
(30)		 88
(31)		 89
(32)		 90
(32)		 92
(33)		 94
(34)		 96
(36)		 98
(37)		 100
(38)		 103
(39)
82
(28)		 81
(27)		 82
(28)		 83
(28)		 84
(29)		 84
(29)		 85
(29)		 86
(30)		 88
(31)		 89
(32)		 90
(32)		 91
(33)		 93
(34)		 95
(35)
80
(27)		 80
(27)		 80
(27)		 81
(27)		 81
(27)		 82
(28)		 82
(28)		 83
(28)		 84
(29)		 84
(29)		 85
(29)		 86
(30)		 86
(30)		 87
(31)

Thanks to NOAA’s National Weather Service for the calculator and to Lans Rothfusz, MIC at NWS Tulsa, Oklahoma for the table.