Vapor Pressure Deficit (VPD) Calculator

Vapor Pressure Deficit (VPD) Calculator

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

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VPD Calculator

Enter your canopy air temperature and relative humidity. Switch to Advanced to include leaf temperature offset and get growth-stage targets.

How to use this calculator
  1. Enter air temperature (°F) at canopy height.
  2. Enter relative humidity (%) at canopy level.
  3. Advanced: add a leaf temp offset and select your growth stage for target comparison.
  4. Tap Calculate VPD — your result appears instantly.
  5. Adjust your environment with humidifiers, dehumidifiers, fans, or AC until VPD is in range.

Target bands: Propagation 0.4–0.8 kPa  ·  Vegetative 0.8–1.2 kPa  ·  Flowering 1.2–1.6 kPa

Frequently Asked Questions

What is VPD and why does it matter for my grow?
VPD describes the drying power of the air around your leaves. When it's in range, plants transpire efficiently — pulling water and nutrients through roots, exchanging CO₂ and O₂, and building tissue faster. Too low and you risk mold, slow growth, and nutrient lock. Too high and plants close their stomata to conserve water, stalling photosynthesis entirely.
Should I use leaf temperature or air temperature?
Leaf temperature gives a more accurate VPD. Leaves typically run 2–3°F cooler than the surrounding air due to evapotranspiration. Use a handheld IR thermometer or a dedicated leaf-VPD monitor at canopy level, then enter the offset in Advanced mode for a more precise result.
What VPD should I target at each growth stage?
General targets: Propagation/Seedling 0.4–0.8 kPa, Vegetative 0.8–1.2 kPa, Flowering 1.2–1.6 kPa. These ranges may shift based on cultivar, CO₂ enrichment, disease pressure, and airflow. Start in the middle of each range and dial in from there.
How do I raise or lower VPD in my grow room?
Raise VPD by lowering RH (add a dehumidifier) or increasing temperature. Lower VPD by raising RH (add a humidifier) or lowering temperature (AC or chiller). Good circulation fans also help create uniform VPD across the canopy and prevent pockets of stale, humid air near dense bud sites.
📊 Interactive VPD Heatmap — See Where You Land Visual ▾
Too Low (< target)
In Target Zone
Too High (> target)
Your reading

Chart shows VPD across all temperature & humidity combinations. Your current reading is plotted as a dot — it updates live as you change inputs above. Hover or tap any cell to see the exact VPD value.
Targets: Propagation 0.4–0.8 · Vegetative 0.8–1.2 · Flowering 1.2–1.6 kPa.

Need help dialing in your environment?

Our grow experts can recommend the right monitors, humidifiers, and controllers for your setup.
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