Heat Index Calculator

This form will calculate the apparent temperature ("heat index") based upon the values you input for actual temperature and humidity. The heat index is an attempt to quantify the effect which high levels of heat and humidity have on the human body.

Temperature (F)
Humidity (%)
Heat Index

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The combined effects of humidity and temperature can pose serious health risks.

Heat Index Danger Level Symptoms
Above 130 Life threatening Heatstroke possible with only brief activity
105 - 130 Extreme danger Heat cramps, exhaustion, headaches after brief activity
90 - 105 Danger Heat cramps, exhaustion, headaches after prolonged activity
80 - 90 Caution Exercise causes fatigue more rapidly

Heat Index Reference Chart




HEAT INDEX 80 - 85
Few people begin to feel uncomfortable.

HEAT INDEX 85 - 90
About half of the people feel uncomfortable.

HEAT INDEX 90 - 104
Sunstroke, heat cramps, and heat exhaustion are possible with prolonged exposure and physical activity..

HEAT INDEX 105 - 129
Sunstroke, heat cramps, or heat exhaustion likely. Heatstroke is possible with prolonged exposure and physical activity.

HEAT INDEX 130 OR HIGHER
Heatstroke or Sunstroke eminent.

Heat Index Chart

Temp          Dew Point(F)
 (F)     50.0  55.0  60.0  65.0  70.0  75.0  80.0  85.0 
--------------------------------------------------------
  65:    62.7  63.8  65.0  66.6                         
  70:    67.8  68.7  69.8  71.1  72.6                   
  75:    73.1  73.9  74.8  75.9  79.2  80.7             
  80:    79.8  80.6  81.6  82.8  84.4  86.9  90.9       
  85:    83.5  84.7  86.1  88.0  90.5  94.0  99.0 106.6 
  90:    87.9  89.4  91.2  93.6  96.9 101.2 107.2 115.6 
  95:    92.9  94.5  96.7  99.6 103.4 108.4 115.2 124.3 
 100:    98.1  99.9 102.4 105.6 109.8 115.3 122.7 132.3 
 105:   103.4 105.4 108.1 111.6 116.1 122.0 129.7 139.7 
 110:   108.7 110.9 113.8 117.5 122.3 128.4 136.3 146.5 

Temp       Relative Humidity (%)
 (F)    90.0  80.0  70.0  60.0  50.0  40.0  30.0  20.0  10.0 
------------------------------------------------------------
  65:   65.6  64.7  63.8  62.8  61.9  60.9  60.0  59.1  58.1 
  70:   71.6  70.7  69.8  68.8  67.9  66.9  66.0  65.1  64.1 
  75:   79.7  76.7  75.8  74.8  73.9  72.9  72.0  71.1  70.1 
  80:   88.2  85.9  84.2  82.8  81.6  80.4  79.0  77.4  76.1 
  85:  101.4  97.0  93.3  90.3  87.7  85.5  83.5  81.6  79.6 
  90:  119.3 112.0 105.8 100.5  96.1  92.3  89.2  86.5  84.2 
  95:  141.8 131.1 121.7 113.6 106.7 100.9  96.1  92.2  89.2 
 100:  168.7 154.0 140.9 129.5 119.6 111.2 104.2  98.7  94.4 
 105:  200.0 180.7 163.4 148.1 134.7 123.2 113.6 105.8 100.0 
 110:  235.6 211.2 189.1 169.4 151.9 136.8 124.1 113.7 105.8 
 115:  275.3 245.4 218.0 193.3 171.3 152.1 135.8 122.3 111.9 
 120:  319.1 283.1 250.0 219.9 192.9 169.1 148.7 131.6 118.2 

Any value less than 80 is considered comfortable.
Any value greater than 90 is considered extreme.
Any value greater than 100 is considered hazardous.
Any value greater than 110 is considered dangerous.

Information from NOAA

Copyright 1997 Scott I. Blanksteen. All rights reserved.