Editing Dew point (section)

===Simple approximation===
There is also a very simple approximation that allows conversion between the dew point, temperature, and relative humidity. This approach is accurate to within about ±1&nbsp;°C as long as the relative humidity is above 50%:
<math display="block">\begin{align}
T_\mathrm{d} &\approx T-\frac{100-\mathrm{RH}}{5}; \\[5pt]
\mathrm{RH} &\approx 100-5(T-T_\mathrm{d});
\end{align}</math>

This can be expressed as a simple rule of thumb:
<blockquote>
For every 1&nbsp;°C difference in the dew point and dry bulb temperatures, the relative humidity decreases by 5%, starting with RH&nbsp;=&nbsp;100% when the dew point equals the dry bulb temperature.
</blockquote>

The derivation of this approach, a discussion of its accuracy, comparisons to other approximations, and more information on the history and applications of the dew point, can be found in an article published in the ''[[Bulletin of the American Meteorological Society]]''.<ref>{{cite journal|author1-link=Mark G. Lawrence|last1=Lawrence|first1=Mark G.|title=The Relationship between Relative Humidity and the Dewpoint Temperature in Moist Air: A Simple Conversion and Applications|journal=Bulletin of the American Meteorological Society|date=February 2005|volume=86|issue=2|pages=225–233|doi=10.1175/BAMS-86-2-225|bibcode=2005BAMS...86..225L|doi-access=free}}</ref> 

For temperatures in degrees Fahrenheit, these approximations work out to
<math display="block">\begin{align}
T_\mathrm{d,^\circ F} &\approx T_\mathrm{{}^\circ F}-\tfrac{9}{25}\left(100-\mathrm{RH}\right);\\[5pt]
\mathrm{RH} &\approx 100-\tfrac{25}{9}\left(T_\mathrm{{}^\circ F}-T_\mathrm{d,^\circ F}\right);
\end{align}</math>

For example, a relative humidity of 100% means dew point is the same as air temp. For 90% RH,  dew point is 3&nbsp;°F lower than air temperature. For every 10 percent lower, dew point drops 3&nbsp;°F.