Free VPD calculator for plant cultivation. Find vapor pressure deficit, view charts, check growth stage targets, and get environment tips.
Tip: Leaf temperature is typically 1-3°C lower than air temperature. Measure with an IR thermometer for accuracy.
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Vapor Pressure Deficit (VPD) is the key metric for controlling plant transpiration and nutrient uptake. Our calculator helps growers dial in perfect environmental conditions by calculating VPD from temperature and humidity, showing optimal ranges for each growth stage, and providing actionable recommendations.
VPD measures the gap between how much moisture the air holds and how much it could hold at saturation, evaluated at the leaf surface — which sets how fast plants transpire, how nutrients move, and how stressed they become. It is derived from the Tetens (1930) saturation-vapor-pressure equation and, by using leaf temperature, gives the true leaf-to-air VPD used in greenhouse climate control (Prenger & Ling, 2001). Unlike relative humidity alone, VPD accounts for temperature.
VPD Formula
Dial in VPD for each growth phase—clones need 0.4-0.8 kPa, veg 0.8-1.2 kPa, flower 1.0-1.5 kPa for maximum yield.
Commercial greenhouses use VPD to automate fog systems, vents, and heating for consistent crop quality.
Control HVAC and dehumidifiers based on VPD targets rather than humidity alone for better results.
Maintain high humidity/low VPD environments for root development without waterlogging media.
VPD directly determines how fast plants lose water through stomata. Optimal VPD maximizes nutrient uptake without causing water stress.
Low VPD creates wet leaf surfaces ideal for powdery mildew, botrytis, and other fungal diseases. Proper VPD keeps foliage dry.
Plants at optimal VPD have fully open stomata, maximum CO2 absorption, and peak photosynthesis rates.
High VPD causes stomata to close, halting growth and causing wilting. The calculator warns you before stress occurs.
The optimal VPD range for vegetative growth is 0.8-1.2 kPa. This allows stomata to remain open for maximum CO2 absorption while maintaining adequate transpiration for nutrient uptake. Early veg can be lower (0.8-1.0 kPa), late veg slightly higher (1.0-1.2 kPa).
VPD occurs at the leaf surface, not in the air. Leaves are typically 1-3°C cooler than air due to transpiration and radiation. Using only air temperature would overestimate VPD. Measure leaf temperature with an infrared thermometer for accuracy.
VPD below 0.4 kPa means transpiration nearly stops. Nutrients aren't transported effectively, calcium deficiency may appear, and wet leaves invite fungal diseases. Increase temperature or decrease humidity to raise VPD.
VPD above 1.5 kPa (flowering) or 1.2 kPa (veg) causes stomata to close as a defense against water loss. This stops photosynthesis, causes wilting, and stunts growth. Lower temperature or increase humidity to reduce VPD.
VPD charts show temperature on one axis and humidity on the other, with colored zones indicating VPD ranges. Find your current temperature and humidity to see which zone you're in. Green zones are optimal, blue zones are too humid, and red zones are too dry.