VPD and environment tracking
Log a reading for any tent: temperature, humidity, CO₂, light (PPFD), pH, EC and light hours. VPD is calculated as you type, and the weekly view shows the trend across the grow.
VPD in kPa by air temperature and humidity
| Air | 50% RH | 60% RH | 70% RH |
|---|---|---|---|
| 22 °C | 1.17 | 0.94 | 0.7 |
| 24 °C | 1.32 | 1.06 | 0.79 |
| 26 °C | 1.49 | 1.19 | 0.9 |
| 28 °C | 1.68 | 1.34 | 1.01 |
Leaf temperature taken as 2 °C below the air.
Frequently asked questions
What is VPD?
Vapour pressure deficit: how much more moisture the air could hold at leaf temperature. It drives how fast the plant transpires, so it tells more than humidity alone.
How is VPD calculated?
Leaf temperature is taken as air temperature minus 2 °C. Saturation pressure at the leaf = 0.61078 × e^(17.27 × T ÷ (T + 237.3)) kPa, and VPD = saturation pressure × (1 − relative humidity ÷ 100). At 26 °C and 60% RH that is 1.19 kPa.
What VPD for veg and flower?
Common targets are about 0.4 to 0.8 kPa for clones and seedlings, 0.8 to 1.2 kPa in veg and 1.2 to 1.6 kPa in flower. Raise VPD by warming the room or lowering humidity; lower it the other way round.