Vapour pressure deficit (VPD) combines temperature and humidity into one number that tells you how strongly plants transpire. Too low and they stall and get mouldy; too high and they close up to save water.
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Enter temperature, humidity and leaf offset. The calculator gives the leaf VPD, the growth zone and the humidity that would hit your target.
SVP(T) = 0.6108 × e^(17.27 T ÷ (T + 237.3)) kPa VPD = SVP(leaf temperature) − SVP(air) × RH RH for target = (SVP(leaf) − target) ÷ SVP(air)
Saturation vapour pressure uses the Tetens equation; temperatures are in °C internally.
At 25 °C and 60% RH, with leaves 2 °C cooler than the air, leaf VPD is about 0.91 kPa: ideal for vegetative growth. For 1.0 kPa you would lower humidity to about 57%.
Around 0.4–0.8 kPa for seedlings, 0.8–1.2 kPa for vegetative growth and 1.2–1.6 kPa for flowering.
Raise humidity or lower the temperature.
Transpiration depends on the vapour pressure inside the leaf, which follows leaf temperature, not air temperature.
Yes. It helps you balance ventilation, heating and humidity to keep plants growing steadily.