Heat Index Chart and Heat Index Calculator
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. |
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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 |
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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.
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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.
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Heat Index Calculator Compliments of National Weather Service |
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