How to Calculate the VPD
- 1). Recognize the components. Saturation and vapor pressure are the two major factors. Saturation is the point at which the air exceeds its absorption and vapor pressure is the amount of water, formed as a gas, which is present in the air.
- 2). Identify the formula. Vapor pressure deficit is defined as vapor pressure saturation minus vapor pressure air. Measure the air temperature and relative humidity and derive the component values.
- 3). Calculate the vapor pressure deficit. For example, if the vapor pressure saturation level was 0.178 psi and the vapor pressure air was 0.142, the resultant vapor pressure deficit would be 0.036 psi.
