VPD Calculator – Optimize Your Grow Room for Maximum Yield
Select which temperature unit you’re using.
Enter grow room or greenhouse air temperature.
Enter the relative humidity percentage.
Leave blank to auto-estimate (usually 1-3°C lower than air temp).
Calculated from saturation vapor pressure – actual vapor pressure.
Shows if VPD is too low, optimal, or too high.
Common ideal VPD ranges for different growth stages:
- Seedlings / Clones: 0.4 - 0.8 kPa
- Vegetative Growth: 0.8 - 1.2 kPa
- Flowering: 1.2 - 1.5 kPa
| Temp (°F) | RH (%) | VPD (kPa) | Status |
|---|---|---|---|
| 75°F | 50% | 1.10 | ✅ Optimal |
| 85°F | 70% | 0.60 | ⚠️ Too Low |
| 80°F | 40% | 1.40 | ⚠️ Too High |
If you have a leaf temperature reading (via infrared thermometer), use it for accurate VPD. If left blank, the tool approximates leaf temperature slightly lower than air temperature.
Warmer leaves can increase transpiration, leading to higher VPD.| Issue | Suggested Fix |
|---|---|
| Low VPD (Too Humid) | Reduce humidity, increase temp, improve ventilation |
| High VPD (Too Dry) | Increase humidity, lower temp, adjust airflow |
Created by James S. Lockwood
With a background in botany and ecological sciences, James specializes in creating practical tools and resources to help gardeners, farmers, and plant enthusiasts optimize their green spaces.
Are you looking for the best VPD (Vapor Pressure Deficit) Calculator to fine-tune your grow room environment? Our VPD calculator helps you achieve optimal VPD levels for seedlings, vegetative growth, and flowering stages, ensuring better transpiration, nutrient uptake, and plant health.
Table of Contents
What is vapor pressure deficit (VPD)?
Vapor Pressure Deficit (VPD) is a measurement that represents the difference between the amount of moisture the air can hold (saturation vapor pressure) and the actual amount of moisture in the air (actual vapor pressure).
In simple terms, VPD tells you how “thirsty” the air is for moisture. It directly affects plant transpiration, nutrient uptake, and overall growth.
Why is VPD Important for Plant Growth?
VPD is one of the most critical factors in controlling humidity and temperature in your grow room, greenhouse, or hydroponic system. Here’s why:
🌱 Too Low VPD (High Humidity)
- Plants don’t transpire enough, leading to poor nutrient uptake.
- Can cause mold, mildew, and root rot.
🔥 Too High VPD (Low Humidity)
- Plants transpire too fast, losing excessive water.
- Can result in wilting, curling leaves, and stress.
✅ Optimal VPD Levels
- Encourage healthy transpiration and nutrient absorption.
- Maximize photosynthesis and plant growth.
How to Calculate VPD?
The VPD formula is based on temperature and relative humidity (RH). Our calculator automatically computes VPD from temperature and humidity to give you real-time insights.
VPD Formula
Where:
- SVP (Saturation Vapor Pressure) depends on air temperature.
- AVP (Actual Vapor Pressure) depends on relative humidity (RH%).
Instead of manually calculating, simply enter your air temperature, relative humidity, and optional leaf surface temperature in our indoor grow VPD calculator, and get instant results.
Why Use a VPD Calculator?
VPD (Vapor Pressure Deficit) is the key to maintaining the right balance between temperature and humidity in your grow room, greenhouse, or indoor garden. Using a vapor pressure deficit calculator, you can prevent issues like slow growth, mold, and excessive water loss while maximizing plant productivity.
VPD Chart for Plants – Grow Room VPD Chart
Find the Right VPD Levels for Each Growth Stage
Different plants require different VPD ranges based on their stage of growth. Use the VPD chart for plants to ensure your humidity and temperature are properly balanced.
Seedlings & Clones
🌱 0.4 – 0.8 kPa VPD
Vegetative Stage
🌿 0.8 – 1.2 kPa VPD
Flowering Stage
🌸 1.2 – 1.5 kPa VPD
Maintaining the right VPD for seedlings and clones will help young plants establish strong roots, while optimizing the VPD for vegetative stage and VPD for flowering ensures vigorous growth and maximum yield.
Leaf Temperature VPD Adjustment
For even more accurate results, adjust VPD based on leaf temperature. Many growers overlook that leaf surface temperature (LST) is slightly lower than air temperature due to transpiration. If you have an infrared thermometer, input your leaf temp into our VPD calculator to fine-tune your values.
How to Calculate VPD from Temperature and Relative Humidity?
- Enter Air Temperature (°C or °F) – This is the ambient temperature of your grow room or greenhouse.
- Enter Relative Humidity (RH%) – This represents the amount of moisture in the air.
- (Optional) Enter Leaf Temperature – For precise calculations, input the actual leaf temp.
- Get Instant VPD Results! – The calculator will provide your VPD value in kPa and indicate whether it’s in the optimal range.
VPD Chart for Greenhouse & Grow Room
The VPD chart greenhouse growers use is similar to indoor grow setups. Greenhouses, however, often have different humidity and temperature fluctuations, making VPD calculations even more crucial.
If your VPD is too low, your plants won’t transpire efficiently, leading to nutrient lockout, weak growth, and mold risks.
If your VPD is too high, plants lose water too quickly, causing wilting and stress.
This chart helps you quickly find the ideal VPD levels based on your grow room’s air temperature and relative humidity. Use it to fine-tune your climate control system for maximum plant health.
70°F
🌡 RH 40%: 1.35 kPa
🌡 RH 50%: 1.08 kPa
🌡 RH 60%: 0.81 kPa
🌡 RH 70%: 0.54 kPa
🌡 RH 80%: 0.27 kPa
75°F
🌡 RH 40%: 1.54 kPa
🌡 RH 50%: 1.24 kPa
🌡 RH 60%: 0.93 kPa
🌡 RH 70%: 0.62 kPa
🌡 RH 80%: 0.31 kPa
80°F
🌡 RH 40%: 1.73 kPa
🌡 RH 50%: 1.39 kPa
🌡 RH 60%: 1.04 kPa
🌡 RH 70%: 0.69 kPa
🌡 RH 80%: 0.35 kPa
85°F
🌡 RH 40%: 1.93 kPa
🌡 RH 50%: 1.55 kPa
🌡 RH 60%: 1.16 kPa
🌡 RH 70%: 0.78 kPa
🌡 RH 80%: 0.39 kPa
90°F
🌡 RH 40%: 2.13 kPa
🌡 RH 50%: 1.71 kPa
🌡 RH 60%: 1.28 kPa
🌡 RH 70%: 0.86 kPa
🌡 RH 80%: 0.43 kPa
How to Use This VPD Chart:
- Find your grow room temperature (°F) in the leftmost column.
- Find your relative humidity (RH%) along the top row.
- The intersecting value is your VPD in kilopascals (kPa).
- Too low? Increase temperature or decrease humidity.
- Too high? Lower temperature or increase humidity.
🌱 For the best plant growth:
- Keep VPD between 0.4 – 1.5 kPa, depending on the growth stage.
- Adjust humidity and temperature for the right transpiration balance
VPD Humidity Relationship – How Humidity Affects VPD?
- Higher humidity = Lower VPD → Risk of mold & slow transpiration.
- Lower humidity = Higher VPD → Risk of over-drying & plant stress.
- Balanced humidity = Optimal VPD Levels → Healthy plant growth.
By using this VPD calculator, you can quickly adjust temperature and humidity to keep your plants in the ideal growing conditions.
Disclaimer for VPD Calculator
This VPD Calculator is for informational and educational purposes only. The results are based on standard VPD formulas and may vary depending on factors such as plant type, environmental conditions, and measurement accuracy.
We do not guarantee specific plant growth outcomes or accept responsibility for crop losses, equipment failure, or incorrect environmental adjustments based on this tool. Always consult professional growers, agronomists, or climate control experts for tailored recommendations.
By using this calculator, you acknowledge that you are responsible for interpreting the data and making adjustments to your grow room or greenhouse settings accordingly.
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