How it's calculated
VPD = SVP(leaf) − SVP(air) × RH ÷ 100, SVP = 0.6108 · e^(17.27 T / (T + 237.3))
T = temperature (°C), SVP = saturation vapor pressure (kPa, Tetens equation), RH = relative humidity (%). SVP(leaf) uses leaf temp (air ± offset), SVP(air) uses air temp; actual vapor pressure = SVP(air)×RH/100. Result in kPa.
Reference ranges
| Growth stage | Target VPD (kPa) |
|---|---|
| Propagation / clones | 0.4 - 0.8 |
| Vegetative | 0.8 - 1.2 |
| Flowering | 1.2 - 1.6 |
| Stress (too dry) | above 1.6 |
Common questions
What is a good VPD for plants?
Most growers aim for 0.8 to 1.2 kPa during the vegetative stage and 1.2 to 1.6 kPa in flowering.
Does VPD use leaf or air temperature?
This tool uses air temperature. If you want leaf-level VPD, subtract about 2 degrees from the air temp to estimate leaf temperature first.