VPD Calculator and Chart

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Ambient air temperature measured at canopy height. 25 °C (77 °F) is a typical vegetative target.
°C
Relative humidity (RH) of the air as a percentage. Use a calibrated hygrometer for accurate readings.
%
Enable to enter a measured leaf surface temperature. Leaf VPD is more accurate than air VPD for predicting actual transpiration. Leaves typically run 1-3 °C cooler than air.
Leaf VPDEarly Vegetative range
0.91kPa

VPD using leaf surface temperature - the most accurate transpiration driver

Air VPD1.27kPa
Saturation VP (air)3.168kPa
Actual VP1.901kPa
Growth stage matchEarly Vegetative range
0.91 kPa
Too low<0.4Propagation0.4-0.8Vegetative0.8-1.2Flower1.2-1.5Too high1.5+

VPD is 0.91 kPa - Early Vegetative range

  • Leaf VPD of 0.91 kPa (Early Vegetative range).
  • Air VPD is 1.27 kPa. The difference of 0.36 kPa reflects the leaf-to-air temperature gap - leaf VPD is the more accurate transpiration driver.
  • This is the sweet spot for vegetative growth (0.8-1.2 kPa). Stomata stay open and CO2 uptake is maximised.
  • Assumes leaf temperature is 2 °C below air (25.0 °C). Measure your leaf surface with an infrared thermometer to get a more precise leaf VPD. Current RH is 60%.

Next stepLog temperature and RH every few hours through the light cycle - VPD often drifts as lights heat the canopy.

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