Humidity calculations
There are methods for calculating and converting between humidity values in terms of dew point, relative humidity, vapour pressure, and all others.
Most humidity calculations involve several steps.
For example, there is no single-step calculation to convert relative humidity to dew point. To do this you would use the air temperature to calculate saturation vapour pressure, then use this with relative humidity to calculate actual vapour pressure, and then use that to calculate dew-point temperature.
Some hygrometer companies provide software for making humidity conversions. This is often a good alternative to struggling with pen, paper and a calculator. Either way, humidity calculations need to be made carefully, with some understanding.
Example: relative humidity can be calculated from vapour pressures as follows:
where
e is the actual vapour pressure of water, and
es is the saturation vapour pressure of water at the actual temperature and pressure.
Humidity calculations are not fully covered here, but are detailed in some of the further reading.
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