VPD (Vapor Pressure Deficit) Calculator
VPD measures the pressure difference between the saturated moisture inside the leaf and the drier surrounding air. Unlike relative humidity (RH) alone, VPD indicates exactly how hard your plants are transpiring.
Estimated Leaf Temperature: 75°F
Perfect balance. Stomata are open, gas exchange is maximized, and nutrients flow smoothly without stress.
Why does leaf temperature offset matter?
Stomata (microscopic pores on the leaves) release water vapor to cool the plant down—a process called transpiration. Because of this evaporative cooling, the temperature of a healthy leaf is usually 2°F to 5°F lower than the surrounding room air.
If your plant is under severe stress, has root disease, or the room is extremely humid, transpiration stops and the leaf temperature rises to match the room air temp (0 offset). For high-accuracy calculations, use an infrared thermometer (temp gun) to measure your canopy leaves and find your exact offset.