Dew point is the temperature the air needs to be cooled to reach 100% relative humidity. At this point, the air can no longer hold water as a gas. As the temperature drops further water drops out of the atmosphere in the form of precipitation, fog and/or condensation forming on the surface of objects exposed to the atmosphere.

If you are seeking to find an estimate of how humid/dry the air will feel, dew point is much better than relative humidity.

## What is relative Humidity?

Relative humidity is the amount of humidity there is in the air relative to the maximum amount there could be. It is expressed as a percentage.

## How to Calculate Dew Point

To calculate dew point, take the air temperature and the relative humidity and run those values through a formula with a common set of values. This particular calculator uses the set of values from the 1974 Psychrometry and Psychrometric Charts, as presented by Paroscientific.

In the below formula, **a** is the air temperature, **h** is the humidity and result is the final output.

A = 17.27 B = 237.7 alpha = ((A * a) / (B + a)) + math.log(h/100.0) result = (B * alpha) / (A - alpha)