Enter the actual vapor density and the saturation vapor density into the calculator to determine the relative humidity.

Relative Humidity Formula

The following formula is used to calculate relative humidity.

RH = VDa / VDs * 100
  • Where RH is the relative humidity (%)
  • VDa is the actual vapor density (g/m^3)
  • VDs is the saturation vapor density (g/m^3)

To calculate relative humidity, divide the actual vapor density by the saturation vapor density.

Relative Humidity Definition

The relative humidity is the ratio of the vapor density to the saturation density of water in the air.

Relative Humidity Example

How to calculate a relative humidity?

  1. First, determine the vapor density.

    Measure the water vapor density.

  2. Next, determine the saturation density.

    Measure the saturation water vapor density.

  3. Finally, calculate the relative humidity.

    Calculate the relative humidity using the formula above.


What is a relative humidity?

The relative humidity is a ratio of vapor density to saturation vapor density. It’s a measure of how much water vapor air can hold compared to how much water vapor it takes to saturate the air at any given temperature.

What is a saturated air?

Saturated air is one at 100% relative humidity and that at the specific temperature it cannot hold any more water vapor.