Vapor Pressure Deficit (VPD) Calculator
Enter air temperature and relative humidity to calculate the vapor pressure deficit (VPD) at both air and leaf level. The result includes dewpoint, absolute humidity, and a colour-coded plant-growth zone indicator.
°C
%
°C
Vapor pressure deficit at the leaf surface — the primary driver of plant transpiration
- 1
Saturation VP — air (Buck)
0.61121 × e^1.64558 = 3.16853Buck (1981) equation for saturation vapor pressure at air temperature. - 2
Actual VP — air
3.16853 × 60 ÷ 100 = 1.90112 - 3
Leaf temperature
25 + 2 = 27 - 4
Saturation VP — leaf (Buck)
0.61121 × e^1.76391 = — - 5
Leaf VPD
— − 1.90112 = 1.665
How does this calculator work?
VPD = eₛ(T) × (1 − RH/100) where eₛ is saturation vapor pressure (kPa) from the Buck equation. Enter air temperature (°C), relative humidity (%), and an optional leaf-temperature offset to get both air and leaf VPD, dewpoint, and a colour-coded plant-growth zone — optimal for most crops is 0.8–1.2 kPa at the leaf.
Formula
How this is calculated
Vapor pressure deficit is the difference between the saturation vapor pressure at a given temperature and the actual vapor pressure of the air: VPD = eₛ(T) − ea. Because ea = eₛ(T) × RH/100, this simplifies to VPD = eₛ(T) × (1 − RH/100). Saturation vapor pressure is calculated using the Buck (1981) equation, which is more accurate than the simple Magnus formula across the range −40 to +60 °C.
In plant science and horticulture a distinction is made between air VPD (computed at ambient temperature) and leaf VPD (computed at the leaf surface temperature, which is typically 1–4 °C warmer than ambient air due to solar radiation absorption). Leaf VPD is the primary driver of transpiration — it is the "pull" on water through the plant's stomata. The adjustable leaf temperature offset lets you model this difference.
VPD zones used by most greenhouse growers are: below 0.4 kPa (too humid, disease risk), 0.4–0.8 kPa (propagation), 0.8–1.2 kPa (vegetative, optimal), 1.2–1.6 kPa (late vegetative/pre-flowering), and above 1.6 kPa (too dry). These are indicative ranges and may be fine-tuned by crop and cultivar.
Frequently asked questions
Most vegetatively growing crops prefer a leaf VPD of 0.8–1.2 kPa. Values below 0.4 kPa risk fungal disease; above 1.6 kPa plants close stomata to conserve water, slowing growth and CO₂ uptake.
Leaf surfaces absorb radiant energy and run warmer than the surrounding air — often 1–4 °C — so the saturation vapor pressure at the leaf is higher. Because the air's actual vapor pressure (ea) is unchanged, the deficit is larger at the leaf than in the bulk air. That higher deficit is what drives water out through stomata.
At 100 % RH the VPD is zero (air is saturated). As RH falls, VPD rises. But VPD also rises with temperature even at constant RH, because warmer air holds exponentially more water vapour at saturation. Two greenhouses at 60 % RH can have very different VPDs if one is at 20 °C and the other at 30 °C.
Also known as
TG we-Calculate Editorial Team. (2026). Vapor Pressure Deficit (VPD) Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/vapor-pressure-deficit-calculator
TG we-Calculate Editorial Team. "Vapor Pressure Deficit (VPD) Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/vapor-pressure-deficit-calculator.
TG we-Calculate Editorial Team, "Vapor Pressure Deficit (VPD) Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/vapor-pressure-deficit-calculator
@misc{wecalculate_vapor_pressure_deficit_calculator, title = {Vapor Pressure Deficit (VPD) Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/vapor-pressure-deficit-calculator}}, year = {2026}, note = {TG we-Calculate} }
Did this calculator help you?