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Relative Humidity Equation

The equation below approximates the relative humidity within 0.6 percent in the range of -25 to 45 o C or -13 to 113 o F. This is the equation used in the javascript calculator.

relative humidity equation

T is equal to the air temperature in degrees Celsius.

Td is equal to the dew point temperature in degrees Celsius.

So in the javascript the equation would be transformed to the following,

Math.round(100.0*(Math.pow((112-(0.1*T)+Td)/(112+(0.9*T)),8))) + "%";

To convert from Fahrenheit to Celsius use,
  • Celsius = (fahrenheit_temperature_value - 32) * 0.556

To conver from Celsius to Fahrenheit use,

  • Fahrenheit = 1.80 * celsius_temperature_value + 32.0

Questions or comments about these pages? Send to Ron Murphy

National Weather Service
Binghamton Weather Forecast Office
32 Dawes Drive
Johnson City, NY 13790
(607) 729-1597
Page last modified: January 9, 2006
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