Posted by GroHaus Cannabis Cultivation Team on Mar 31st 2025
What Is VPD? Ideal Vapor Pressure Deficit Chart for Cannabis Growers
What Is VPD? Chart for Cannabis Growers
VPD (Vapor Pressure Deficit) is one of the most overlooked—but most powerful—tools in your grow room. It helps you balance temperature and humidity to optimize plant health, transpiration, and yield.
What Is VPD?
VPD stands for Vapor Pressure Deficit. It measures how much moisture the air can "pull" from your plants. If the air is too dry, plants can over-transpire. If it’s too humid, they can’t transpire enough—and growth slows down.
VPD is measured in kilopascals (kPa). The ideal range changes depending on your plant’s stage of growth.
Ideal VPD Ranges by Stage
- Seedlings: 0.6–0.9 kPa
- Veg: 0.9–1.2 kPa
- Flower: 1.2–1.6 kPa
How to Read a VPD Chart
Use a thermometer and hygrometer to find your current temp and humidity. Then locate those values on the VPD chart to see if you’re in the optimal zone.
Here’s a sample chart you can use:
| Temp (°F) | 40% RH | 50% RH | 60% RH | 70% RH | 80% RH |
|---|---|---|---|---|---|
| 68°F | 1.10 | 0.92 | 0.73 | 0.55 | 0.37 |
| 72°F | 1.23 | 1.03 | 0.82 | 0.62 | 0.41 |
| 75°F | 1.32 | 1.10 | 0.88 | 0.66 | 0.44 |
| 78°F | 1.42 | 1.18 | 0.95 | 0.71 | 0.47 |
| 82°F | 1.56 | 1.30 | 1.04 | 0.78 | 0.52 |
Use our free VPD Calculator to fine-tune your grow space.
How to Adjust VPD in Your Grow Room
- Too low VPD? Lower humidity or raise temperature
- Too high VPD? Raise humidity or lower temperature
- Use: humidifiers, dehumidifiers, AC, fans, or controllers
Pro tip: Keep air movement steady to avoid microclimates that throw off VPD readings.
Recommended Tools
Keep Learning
Mastering VPD is just one part of dialing in your grow. Learn more about:
- Best temps and humidity for each stage
- How VPD affects yield and quality
- Tools to automate your environment
Tool & guide by GrōHaus — helping growers dial in their environment, light, and yield.