Cannabis VPD Calculator
Calculate vapor pressure deficit to optimize your grow room environment for healthier plants and bigger yields.
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VPD Zones Reference
Recommended VPD by Growth Stage
| Stage | VPD (kPa) | Temp (°F) | RH (%) |
|---|---|---|---|
| Seedling / Clone | 0.4 – 0.8 | 72 – 78 | 65 – 75 |
| Early Veg | 0.8 – 1.0 | 75 – 82 | 55 – 65 |
| Late Veg | 1.0 – 1.2 | 75 – 82 | 50 – 60 |
| Early Flower | 1.0 – 1.3 | 75 – 80 | 45 – 55 |
| Late Flower | 1.2 – 1.6 | 72 – 78 | 40 – 50 |
What Is VPD?
Vapor Pressure Deficit (VPD) measures the difference between the amount of moisture in the air and the maximum amount of moisture the air can hold at a given temperature. It is expressed in kilopascals (kPa) and is one of the most important environmental parameters for cannabis cultivation.
VPD directly controls how fast your plants transpire — the process of pulling water and nutrients from the roots through the plant and releasing water vapor through the stomata on the leaves. When VPD is dialed in correctly, your plants achieve optimal nutrient uptake, stronger cell structure, and faster growth.
Low VPD (below 0.4 kPa) means the air is nearly saturated. Plants struggle to transpire, leading to slow nutrient uptake, calcium deficiencies, and high risk of mold and mildew. Condensation on leaves creates a breeding ground for pathogens.
High VPD (above 1.6 kPa) means the air is very dry relative to temperature. Plants transpire excessively, causing stress, stomatal closure, and nutrient lockout. Leaves may curl, wilt, or develop burnt edges.
The VPD Formula
SVP(T) = 0.61078 × e^((17.27 × T) / (T + 237.3))
where T is temperature in °C
VPD = SVP(leaf temp) − (SVP(air temp) × RH / 100)
Leaf temp is typically ~2°C below air temperature
By manipulating temperature and humidity together using this calculator, you can target the perfect VPD for each stage of growth — giving your cannabis plants the ideal conditions to thrive from seedling to harvest.
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