Enter the water vapor pressure and the water vapor temperature into the calculator to determine the absolute humidity.

Absolute Humidity Formula

The following formula is used to calculate the absolute humidity of the air.

AH = Pw / (R*T)
  • Where AH is the absolute humidity
  • Pw is the water vapor pressure
  • R is the gas constant for water vapor (461.5)
  • T is the temperature (C)

To calculate the absolute humidity, divide the water vapor pressure by the product of the gas constant and air temperature.

Absolute Humidity Definition

What is absolute humidity? Absolute humidity is a measure of the total mass of water vapor per unit of volume of water vapor in the air at any given time.

This is opposed to relative humidity which is the amount of water vapor in the area relative to temperature.

Example Problem

How to calculate absolute humidity?

First, determine the water vapor pressure. If you are unsure of how to determine this, visit the water vapor pressure calculator linked above.

For this example, the pressure is found to be 50.

Next, determine the ambient air temperature.

For this example, the temperature is 25C.

Finally, calculate the absolute humidity using the formula above:

AH = 50/ (461.5* AH = Pw / (R*T)

AH = 50/ (461.5*25) = 50/11537.5

AH = .0043.


Is absolute humidity dependent on temperature? Absolute humidity is a function of temperature. This can be seen in the formula for calculating absolute humidity. AH = Pw/(R*T), where T is the temperature of the air.

As temperature increases, the absolute humidity will decrease. As temperature decreases, the absolute humidity will increase.

Is absolute humidity a percentage? Absolute humidity is not a percentage.

Relative humidity on the other hand is a percentage relative to temperature.

Does absolute humidity change with pressure? Yes, as we saw with temperature, absolute humidity is directly correlated to the water vapor pressure.

As pressure increases, the absolute humidity will also increase, and vice versa for decreasing pressures.