Heat Index

Equivalent heat index - temperature vs relative humidity - in degrees Fahrenheit and Celsius

The heat index can be used to indicate how an average person will perceive temperature and humidity and the human body ability to cool it self.

Heat Index in degrees Fahrenheit

The heat index in degrees Fahrenheit can be calculated as

tHI = -42.379 + 2.04901523 t + 10.14333127 φ

    - 0.22475541 t φ - 0.00683783 t2 - 0.05481717 φ2

    + 0.00122874 t2 φ + 0.00085282 t φ2 - 0.00000199 (T φ)2                                         (1)

where

tHI = heat index (oF)

t = air temperature (oF) (t > 57oF)

φ = relative humidity (%)

Heat index diagram in degrees fahrenheit

Apparent Temperature Heat Stress Index (oF)
Relative Humidity
(% RH)
Temperature (oF)
80859095100105110115120125130135140
0 78 82 87 911) 94 97 100 103 105 107 108 110 110
5 78 82 86 90 94 98 102 106 110 114 117 121
10 78 82 86 902) 95 100 105 110 116 121 128
15 78 82 86 91 96 102 108 115 122 130
20 79 82 86 91 97 104 112 121 130 140
25 79 82 87 93 100 108 117 127 138
30 79 83 88 94 102 112 122 134 148
35 80 84 89 96 106 116 129 143
40 80 84 91 99 109 121 136 152
45 80 85 92 102 114 127 143
50 81 86 95 1053) 118 134 152
55 81 88 97 109 124 141
60 82 89 100 113 129 149
65 82 91 103 118 136
70 83 93 106 123 143
75 84 95 109 1284)
80 84 97 113 134
85 85 99 117
90 86 102 122
95 86 104
100 87 107
  • T(oC) = 5/9[T(oF) - 32]

Sunstroke and heat exhaustion:

1) Caution - Fatigue is possible with prolonged exposure and/or physical activity

2) Extreme Caution - Sunstroke, heat cramps and heat exhaustion are possible with prolonged exposure and/or physical activity

3) Danger - Sunstroke, heat cramps and heat exhaustion are likely. Heat stroke is possible with prolonged exposure and/or physical activity

4) Extreme Danger - Heatstroke/sunstroke is highly likely with continued exposure

Heat Index in degrees Celsius

Heat index in degrees Celsius:

Heat index diagram - in degrees celsius

Related Topics

  • Physiology - Human physiology, air quality and comfort temperatures, activity and metabolic rates, health effects of carbon monoxide and more
  • Air Conditioning - Air Conditioning systems - heating, cooling and dehumidification of indoor air for thermal comfort

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