VPD Calculator (Vapor Pressure Deficit)
Calculate Vapor Pressure Deficit (VPD) from air temperature, leaf temperature and relative humidity to help dial in the ideal growing environment for your plants.
What Is Vapor Pressure Deficit?
Vapor Pressure Deficit (VPD) is the difference between the amount of moisture the air can hold when fully saturated and the amount of moisture actually in the air. It is widely used by growers because it drives how easily a plant’s leaves transpire (release water vapor), which in turn affects nutrient uptake and growth rate.
How This Calculator Works
The calculator estimates the saturation vapor pressure at both air temperature and leaf temperature using the Tetens/Magnus approximation, then subtracts the actual vapor pressure (based on relative humidity) from the leaf-temperature saturation value. Leaf temperature is estimated as the air temperature minus the offset you provide, since leaves are typically 1-4 degrees cooler than the surrounding air due to transpirational cooling.
Reading Your Result
Common target ranges are roughly 0.4-0.8 kPa for clones and early vegetative growth, 0.8-1.2 kPa for late vegetative growth, and 1.2-1.6 kPa for flowering or fruiting stages, though optimal ranges vary by species. This tool is intended for general growing guidance and educational purposes, not as a substitute for species-specific agronomic advice.
Note: Actual leaf temperature depends on airflow, light intensity and plant health, so treat the leaf offset as an estimate unless you are measuring leaf temperature directly with an infrared thermometer.