Dew Point

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The dew point is the temperature at which dew would start to form, and depends on the present temperature and relative humidity. 

The drier the air, the less water it holds, so it has to be a lot colder to condense as dew. So in very damp conditions, with high relative humidity, the dew point is only a little lower than the ambient temperature.

 

Relative Humidity % 

deg C

10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
25 -8.7 0.5 6.2 10.4 13.8 16.7 19.1 21.3 23.2 25.0
20 -12.5 -3.6 1.9 6.0 9.3 12.0 14.4 16.4 18.3 20.0
15 -16.4 -7.8 -2.4 1.5 4.7 7.3 9.6 11.6 13.4 15.0
10 -20.2 -11.9 -6.8 -3.0 0.1 2.6 4.8 6.7 8.4 10.0
5 -24.1 -16.1 -11.1 -7.5 -4.6 -2.1 -0.0 1.8 3.5 5.0
0 -28.0 -20.3 -15.5 -12.0 -9.2 -6.8 -4.8 -3.0 -1.4 0.0
-5 -31.9 -24.5 -19.9 -16.5 -13.8 -11.5 -9.6 -7.9 -6.4 -5.0
-10 -35.8 -28.7 -24.3 -21.0 -18.4 -16.3 -14.4 -12.8 -11.3 -10.0

Yes there is a formula for dew point, in fact I've found two which are both on an Excel file you can download, just right mouse click on this link and Save Target As...

Also, if you wish to find dew point directly from wet and dry bulb temperature readings click on this link and Save Target As...

Put your own temperature and relative humidity into the blue boxes, then the dew point will be calculated in the yellow and the green boxes (by different methods).  The table above is based on the yellow calculation.

 

 

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