Enter the saturated vapor pressure and the vapor pressure of the air into the calculator to determine the vapor pressure deficit (VPD).

## VPD Formula

The following formula is used to calculate a vapor pressure deficit.

VPD = SVP – AVP

• Where VPD is the vapor pressure deficit
• SVP is the saturated vapor pressure
• AVP is the actual vapor pressure

To calculate the saturated vapor pressure, visit the water vapor pressure calculator linked above.

The VPD can also be calculated using the saturated vapor pressure and the relative humidity with this formula:

VPD = SVP * (1-RH/100) = VPD

• Where RH is the relative humidity (%)

## Vapor Pressure Deficit Definition

A vapor pressure deficit, or VPD for short, is the difference between the saturated vapor pressure and the actual current vapor pressure.

The saturated vapor pressure is the maximum amount of water vapor a body of air at a given temperature can hold.

## Example Problem

How to calculate VPD?

1. First, determine the actual water vapor pressure.

For this example, the air is found to have a water vapor pressure of 1.45 kPa (kilo-pascals).

2. Next, determine the saturated water vapor pressure.

For this problem, the saturated vapor pressure is found to be 2.14 kPa.

3. Finally, calculate the VPD.

Using the formula above, the VPD is calculated as:
VPD = SVP – AVP
VPD = 2.14 – 1.45
VPD = .69 kPa