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.