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Vapour Pressure Deficit Calculator

Work out vapour pressure deficit instantly with clear inputs, formula shown and shareable results.

About Vapour Pressure Deficit Calculator

Vapour pressure deficit is the gap between saturation and actual vapour pressure, and it drives transpiration far more directly than relative humidity does. Leaves usually sit a couple of degrees below air temperature, which lowers their saturation pressure and the deficit they experience. Growers target 0.8-1.2 kPa leaf VPD for most crops.

Formulas

Vapour pressure deficit

VPD = es(leaf temperature) - ea(air)

Actual vapour pressure

ea = RH / 100 x es(air temperature)

Worked example

With the default values below, Vapour Pressure Deficit Calculator returns Leaf Vapour Pressure Deficit of 0.797. Change any input above and every figure here is recalculated in your browser.

Inputs used

Air temperature
26 C
Relative humidityaccepts 0–100 %
65 %
Leaf temperature offset
-2 C

Results

Leaf Vapour Pressure Deficit
0.797 kPa
Air Vapour Pressure Deficit
1.174 kPa
Saturation Vapour Pressure
3.353 kPa
Growing Assessment
Low - suits propagation and young plants

Step by step

  1. 1Values used
  2. 2Vapour pressure deficit
  3. 3Actual vapour pressure
  4. 4Leaf Vapour Pressure Deficit= 0.797 kPa
  5. 5Air Vapour Pressure Deficit= 1.174 kPa
  6. 6Saturation Vapour Pressure= 3.353 kPa
  7. 7Growing Assessment= Low - suits propagation and young plants

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why use leaf rather than air temperature?

Because transpiration is driven by the deficit at the leaf surface, and transpirational cooling keeps leaves below air temperature.

What happens at very high VPD?

Stomata close to conserve water, which stops carbon dioxide uptake and halts growth even when light and nutrients are ample.

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