VPD Calculator for Grow Rooms

Calculate VPD (Vapor Pressure Deficit) and see how it interacts with your light intensity. VPD is the single most important environmental variable for maximising plant growth alongside PPFD.

VPD and light are linked: Higher PPFD drives more transpiration, which requires higher VPD to keep stomata open and CO2 flowing. At low light, high VPD stresses plants. At high light, low VPD limits photosynthesis. This calculator accounts for your actual PPFD when assessing VPD.
Temperature units
Grow room conditions
Affects optimal VPD range
Growth stage
Seedling
0.4-0.8 kPa
Vegetative
0.8-1.2 kPa
Early Flower
1.0-1.5 kPa
Late Flower
1.5-2.0 kPa

Please enter temperature and humidity.

Vapor Pressure Deficit
0 kPa
0
Sat. vapor pressure (kPa)
0
Actual vapor pressure (kPa)
0
Leaf temp used (F)
VPD scale — 0 to 3.0 kPa
0 Too low0.81.21.83.0 Too high
Air temperature
Leaf temperature
Relative humidity
PPFD
Calculated VPD
Target VPD for stage
VPD adjusted for PPFD
How to reach target VPD
VPD chart — temp vs humidity (kPa) — your reading marked
Shop grow room temperature and humidity controllers on Amazon

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The calculators and tools on LightingCalc.lighting are provided for general guidance and informational purposes only. Results are estimates based on standard formulas and the values you enter — they do not constitute professional engineering, electrical, or architectural advice. Always verify calculations with a qualified professional before making decisions for any safety-critical, code-compliance, or commercial application. LightingCalc.lighting makes no representations or warranties as to the accuracy or completeness of any result, and accepts no liability for errors, omissions, or any outcomes arising from reliance on this information.