Vapor Pressure Deficit (VPD) Calculator

Dial in temperature and humidity for healthier transpiration and faster growth. Use Simple for quick checks—or Advanced to add leaf temp offset and stage targets. Prefer help? Talk to a Grow Expert.

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Vapor Pressure Deficit (VPD) Calculator

Find your grow room’s VPD instantly. Start in Simple; switch to Advanced to add leaf temp offset and growth stage targets.

Air Temp (°F) i Canopy-level air temp. Place your probe at plant height for accuracy.

Relative Humidity (%) i Room RH. Typical range is 40–70% depending on stage and disease pressure.

Leaf Temp Offset (°F) i Leaves are often ~2–3°F cooler than air. Enter a negative value (e.g., -3).

Growth Stage

How to use this calculator (step-by-step)

Enter air temperature (°F) measured at canopy height.
Enter relative humidity (%).
Advanced: add a leaf offset (°F) and select growth stage.
Calculate to get VPD (kPa) and see your status vs targets.
Adjust temp/RH with humidifier, dehumidifier, fans, or AC.

Target bands: Propagation: 0.4–0.8 • Veg: 0.8–1.2 • Flower: 1.2–1.6 kPa.

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Frequently Asked Questions

What is VPD and why does it matter?

VPD describes the drying power of air around leaves. Keeping VPD in range improves transpiration, nutrient uptake, and disease resistance.

Should I use leaf temperature or air temperature?

Using a leaf temp offset (often −2 to −3°F vs air) gives a more accurate VPD than air temp alone.

What VPD should I target for each stage?

Propagation 0.4–0.8, Veg 0.8–1.2, Flower 1.2–1.6 kPa. Adjust for cultivar, CO₂, and disease pressure.

How do I raise or lower VPD?

Raise VPD by lowering RH or raising temp; lower VPD by raising RH or lowering temp. Tools: humidifiers, dehumidifiers, fans, AC.

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Vapor Pressure Deficit (VPD) Calculator

Vapor Pressure Deficit (VPD) Calculator

Frequently Asked Questions

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