AN607

28

Rev. 1.7

Equation Comparison

The following graph compares the above equations:

Mark Lawrence Rule of Thumb*

This easy to use equation provides an estimate of change in dew point for a change in relative humidity or can be

easily reversed to estimate a change in relative humidity for a known change in dew point. This approximation is

valid for RH>50%. This rule of thumb says that the dew point temperature decreases approximately 1C for every

5% decrease in RH starting at tdp = t and RH=100%. This relationship is very handy if very little computational

capability is available and the accuracy limitations and range of applicability are acceptable.

*Note: See Lawrence, Mark G., “The Relationship between Relative Humidity and the Dewpoint Temperature in Moist Air - A

Simple Conversion and Applications”, American Meteorological Society February 2005.

Td

B

RH

100

----------





A

B

1

T

+

----------------

+

A

1

In

RH

100

----------





–

A

B

1

T

+

----------------

–

---------------------------------------------------------

=