VPD Calculator
Calculate Vapour Pressure Deficit from temperature and humidity
°C
Leave blank to match most controllers (air VPD). Enter a lower value for leaf VPD.
%
-
kPa
VPD Reference Zones
| Range (kPa) | Stage | Notes |
|---|---|---|
| < 0.4 | Too low | High disease risk, slow transpiration |
| 0.4 - 0.8 | Propagation / clones | Reduced stress for cuttings and seedlings |
| 0.8 - 1.2 | Vegetative | Ideal for leafy growth |
| 1.2 - 1.6 | Flowering / fruiting | Higher transpiration drives nutrient uptake |
| > 1.6 | Too high | Heat stress, stomatal closure |
Method: SVP calculated using the Magnus formula. VPD = SVPleaf - (RH/100 × SVPair). When no leaf temperature is entered, leaf temperature equals air temperature (air VPD), matching most grow-room controllers. Enter a lower leaf temperature for leaf VPD, which is often 1-2°C below air under grow lights.
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