Vapor Pressure Deficit Calculator

Use this calculator to find how dry the air is compared with saturation, a key greenhouse and indoor-growing driver. Enter the air temperature and relative humidity. Plants transpire against VPD: too low and the crop stays wet; too high and it stresses.

Saturation vapour pressure is computed with the Tetens formula at your temperature. Actual vapour pressure is that value times relative humidity over 100. VPD is the difference, in kilopascals (kPa). Temperature can be entered in Celsius (°C) or Fahrenheit (°F); Fahrenheit is converted to Celsius before Tetens is applied. Relative humidity is a percent: type 60 for 60%.

This is air VPD, not a leaf-temperature correction. Leaf VPD uses leaf temperature instead of air temperature and is often a little different. Typical greenhouse targets are often around 0.8–1.2 kPa, depending on crop and stage.

Air temperature: Temperature of the room or greenhouse air. Enter the value in °C or °F.

Relative humidity (%): Relative humidity as a percent from 0 to 100.

VPD: Air vapor-pressure deficit in kilopascals.