# Absolute Humidity

Written by Jerry Ratzlaff on . Posted in Thermodynamics

Absolute humidity, abbreviated as AH, of the air is the concentration of water vapour expressed as the weight of water in unit volume of space.  In an isolated space this does change with pressure, because the space shrinks under pressure, pushing the water molecules closer together.

## Absolute Humidity formula

 $$\large{ AH = \frac{ m_v }{ V } }$$

### Where:

 Units English Metric $$\large{ AH }$$ = absolute humidity $$\large{\frac{lbm}{ft^3}}$$ $$\large{\frac{g}{m^3}}$$ $$\large{ m_v }$$ = mass of water vapor $$\large{lbm}$$ $$\large{ kg}$$ $$\large{ V }$$ = volume of air $$\large{ ft^3 }$$ $$\large{ m^3 }$$