VPD Calculator
Enter your grow room’s temperature and humidity, pick a growth stage, see whether your plants are in the transpiration zone they should be.
Your plants are comfortable. Transpiration is balanced — stomata open, water moving, nutrients following.
Seedling target
Veg target
Flower target
What is VPD?
Vapour Pressure Deficit measures how “thirsty” the air is for water. It’s the gap between how much water the air is holding and how much it could hold at that temperature.
When VPD is right, your plants transpire efficiently: stomata open, water climbs up the xylem, nutrients hitch-hike with it, CO₂ diffuses in. When VPD is too low, the air is “full” and plants slow down — risk of mould, stretching, inefficient growth. Too high and plants close their stomata to conserve water, starving themselves of CO₂.
The calculator uses the Magnus-Tetens equation against your current temperature and relative humidity:
VPD = 0.6108 · e^((17.27·T)/(T+237.3)) · (1 − RH/100)
Assumes leaf temperature ≈ air temperature. In a well-ventilated tent that’s usually within 1°C. With CO₂ enrichment or sealed rooms, leaves can sit 2–3°C below air — use a dedicated leaf-temp probe for accuracy.
Automate it
The BudMaster Nexus measures VPD in real time from industrial sensors and modulates your fans, heaters and dehumidifiers to hold your target through the entire photoperiod. Seedling, veg, flower and late-flower presets built in. No cloud, no subscription.
See the BudMaster Nexus →