VPD Calculator (Vapor Pressure Deficit)
Turn your air temperature and relative humidity into the number that controls how fast your plants drink and transpire—and see exactly what humidity level you need to hit your crop’s target VPD.
- Magnus-Tetens physics equation
- Runs 100% in-browser
- Leaf offset support
Calculate Your VPD
Enter your grow room environment parameters below.
Your VPD Level
Fill in your grow space environment and click Calculate VPD to view transpiration metrics.
How the VPD Calculator Works
VPD measures the atmospheric drying power pulling moisture through your plants.
1. Saturation Pressure (SVP)
Warmer air holds more water vapor. The saturation vapor pressure at leaf surface temperature defines maximum 100% moisture capacity.
2. Actual Vapor Pressure (AVP)
Relative humidity indicates how much moisture is currently held. Saturation pressure multiplied by RH percentage gives actual air vapor pressure.
3. Vapor Deficit (VPD = SVP – AVP)
Subtracting air vapor pressure from leaf saturation pressure yields VPD in kilopascals (kPa). A higher deficit accelerates transpiration.
Target VPD by Crop Category & Stage
Optimal kilopascal (kPa) targets measured at canopy height.
| Crop / Growth Stage | Target VPD (kPa) |
|---|---|
| Seedlings & Clones | 0.4–0.8 kPa |
| Leafy Greens & Microgreens | 0.8–1.1 kPa |
| Culinary Herbs | 0.8–1.2 kPa |
| Fruiting Crops (Tomato, Pepper, Cucumber) | 1.0–1.5 kPa |
| Eggplant (Vegetative Stage) | 0.8–1.1 kPa |
| Melons (Fruiting Stage) | 1.2–1.6 kPa |
Frequently Asked Questions
What is VPD in hydroponic and indoor growing?
Vapor Pressure Deficit (VPD) is the difference in kilopascals (kPa) between the moisture pressure inside saturated plant leaves and the moisture pressure of the surrounding room air. It directly controls stomatal opening, transpiration rate, and nutrient solution uptake.
How do you calculate VPD?
Calculate saturation vapor pressure at leaf temperature using the Magnus equation: SVP = 0.6108 × e(17.27 × T / (T + 237.3)). Then calculate air vapor pressure (AVP = SVPair × (RH / 100)). Finally, subtract AVP from leaf SVP (VPD = SVPleaf - AVP).
What is an ideal VPD range for most plants?
Leafy greens thrive between 0.8–1.1 kPa, fruiting crops prefer 1.0–1.5 kPa, and flowering plants function best at 1.2–1.6 kPa. Delicate unrooted clones require a low 0.4–0.8 kPa to prevent wilting.
Should I use leaf temperature or room air temperature?
Ideal VPD calculations use leaf surface temperature. Under intense grow lighting, leaves typically run 1–2°C warmer than ambient room air due to radiation absorption. If measuring leaf temperature directly with an IR thermometer, set leaf offset to 0.
Why is VPD more useful than Relative Humidity (RH)?
Relative humidity varies continuously with temperature fluctuations. VPD combines temperature and humidity into a single absolute physical value predicting plant transpiration rate, allowing consistent climate control even as room temperatures shift.
How do I raise or lower my grow room VPD?
If VPD is too high (dry air): increase room humidity using a humidifier or lower room temperature. If VPD is too low (humid air): run a dehumidifier, increase exhaust ventilation, or raise room temperature.
Looking for Something Else?
Browse every calculator and tool MistCulture offers for soilless and indoor vertical farmers.
Disclaimer: Target ranges are general guidelines. Actual optimum VPD varies by cultivar, light intensity, and stage. © MistCulture.com