This calculator requires the use of Javascript enabled and capable browsers. This script (actually 4 calculators) calculates the Heat Index from the relative humidity or from the dew point, along with the ambient air temperature in degree Fahrenheit (F) or Celsius (C). In the selected calculator, enter the temperature in F or Cand the other factor (numeric entry only); then click on Calculate. The calculator will return the Heat Index and other relative information. You may independently clear the values of any calculator to start over. The heat Index does not really occur below 85 degrees F (30 degrees C).