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Calculate vapor pressure deficit for optimal plant transpiration and growth
Air Temperature (°F)
Relative Humidity
Leaf Temp Offset (°F)
Leaves are typically 2-5°F cooler than air
Growth Stage
1.07
kPa
Target: 0.8 – 1.2 kPa for veg
Your environment is dialed in for vegetative growth.
VPD Heatmap
Detailed Values
SVP (air)
3.274 kPa
SVP (leaf)
2.867 kPa
AVP
1.801 kPa
Dew Point
60°F
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Create Free Account →Vapor Pressure Deficit (VPD) measures the difference between the amount of moisture in the air and the maximum moisture the air can hold at a given temperature. Unlike relative humidity alone, VPD accounts for temperature, giving you a more accurate picture of how your plants experience their environment.
When VPD is in the optimal range, plants transpire efficiently — pulling water and dissolved nutrients up through their roots and out through their leaves. Too low, and transpiration slows, increasing the risk of mold. Too high, and plants close their stomata to conserve water, reducing growth and causing stress.
| Stage | Target VPD (kPa) | Notes |
|---|---|---|
| Seedling/Clone | 0.4 – 0.8 | Low transpiration, high humidity |
| Vegetative | 0.8 – 1.2 | Active growth, moderate transpiration |
| Flowering | 1.2 – 1.6 | Strong transpiration, lower humidity |
55% relative humidity means very different things at different temperatures. At 70°F, 55% RH produces a VPD of about 0.8 kPa — fine for vegetative growth. But at 85°F, 55% RH produces a VPD of 1.4 kPa — borderline stress. VPD combines temperature and humidity into a single number that directly correlates with how hard your plants are working to transpire.
What is a good VPD for growing?
The ideal VPD depends on growth stage. Seedlings thrive at 0.4-0.8 kPa, vegetative plants at 0.8-1.2 kPa, and flowering plants at 1.2-1.6 kPa.
How do I measure leaf temperature?
Use an infrared (IR) thermometer pointed at the leaf surface. Measure several leaves at canopy level and average the readings.
Does VPD matter in soil growing?
Yes. VPD affects transpiration regardless of growing medium. Proper VPD helps plants pull water and nutrients through their roots.
What VPD causes mold?
Mold risk increases when VPD drops below 0.4 kPa, indicating very high humidity relative to temperature. Keep VPD above 0.4 kPa to reduce risk.
Theme
Width
Height (px)
<iframe src="https://growmeridian.com/embed/vpd-calculator" width="100%" height="500" frameborder="0" style="border-radius:12px;" title="vpd calculator"></iframe>
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