VPD (Vapor Pressure Deficit) Calculator
Calculate Vapor Pressure Deficit for grow rooms, greenhouses, and indoor gardens. Optimize temperature and humidity for plant health and yield.
VPD Result
Environment Details
VPD Classification
VPD Reference Chart (kPa)
| Temp (°C) | RH 40% | RH 50% | RH 60% | RH 70% | RH 80% |
|---|
Seedling Stage
- VPD Range: 0.4 - 0.8 kPa
- Optimal: 0.6 kPa
- Humidity: 70-80%
- Temperature: 72-78°F
Vegetative Stage
- VPD Range: 0.8 - 1.2 kPa
- Optimal: 1.0 kPa
- Humidity: 60-70%
- Temperature: 72-78°F
Flowering Stage
- VPD Range: 1.0 - 1.5 kPa
- Optimal: 1.2 kPa
- Humidity: 50-60%
- Temperature: 68-75°F
Frequently Asked Questions
What is VPD (Vapor Pressure Deficit)?
Vapor Pressure Deficit (VPD) is the difference between the amount of moisture in the air and the maximum amount of moisture the air can hold at a given temperature. It's a critical metric for plant growth, affecting transpiration, nutrient uptake, and overall health.
How is VPD calculated?
VPD = SVP × (1 - RH/100)
Where SVP is the Saturated Vapor Pressure at the given temperature, and RH is Relative Humidity.
What is the ideal VPD for cannabis?
Ideal VPD for cannabis varies by growth stage:
- Seedling: 0.4 - 0.8 kPa
- Vegetative: 0.8 - 1.2 kPa
- Flowering: 1.0 - 1.5 kPa
What happens if VPD is too high?
High VPD (>1.5 kPa) causes rapid transpiration, leading to:
- Stomata closure
- Reduced photosynthesis
- Nutrient burn symptoms
- Increased water usage
What happens if VPD is too low?
Low VPD (<0.4 kPa) causes reduced transpiration, leading to:
- Nutrient deficiencies
- Mold and mildew risk
- Slow growth
- Root problems
How do I fix my VPD?
To adjust VPD:
- To increase VPD: Raise temperature, lower humidity, or both
- To decrease VPD: Lower temperature, raise humidity, or both
- Use humidifiers, dehumidifiers, heaters, or air conditioners
Is VPD the same as humidity?
No. Humidity (relative humidity) is one factor in VPD. VPD also depends on temperature. The same humidity at different temperatures results in different VPD values. VPD is a more complete measure of plant stress than humidity alone.
What's the difference between VPD and dew point?
VPD measures how "thirsty" the air is for moisture. Dew point is the temperature at which air becomes saturated with moisture. VPD is more relevant for plant growth because it directly affects transpiration rates.
What is the best VPD for seedlings?
Seedlings thrive with VPD between 0.4-0.8 kPa. Higher humidity (70-80%) and moderate temperatures help delicate seedlings develop properly. Avoid VPD above 1.0 kPa for seedlings.
Can I use VPD for outdoor growing?
Yes! VPD is relevant for all plant environments. For outdoor plants, VPD helps you understand when conditions might be stressing your plants, helping you decide when to water or provide shade.