Calculator
Enter temperature and humidity, then compare against your chosen stage target.
Example data table
| Temperature (°C) | Relative Humidity (%) | VPD (kPa) |
|---|---|---|
| 24 | 60 | 1.1936 |
| 27 | 50 | 1.7827 |
| 22 | 70 | 0.7932 |
Formula used
This calculator estimates Vapor Pressure Deficit (VPD) from temperature and relative humidity. First, it calculates Saturation Vapor Pressure (SVP) at the chosen effective temperature:
Then it estimates Actual Vapor Pressure (AVP) using relative humidity (RH):
Finally, VPD is the difference between SVP and AVP:
Practical note: VPD is a climate indicator. It does not replace airflow, lighting, or irrigation checks.
How to use this calculator
- Choose your units and enter relative humidity.
- Select a temperature basis: air, leaf, or air plus offset.
- Enter the required temperature fields for your chosen mode.
- Select a growth stage target range for quick comparison.
- Press Calculate VPD to see results above the form.
- Download a CSV or PDF report to keep your records.
VPD management guide for garden environments
1) What the numbers mean
Vapor Pressure Deficit (VPD) is the “drying power” of air around leaves. This tool calculates SVP from temperature, then AVP from relative humidity, and reports VPD in kPa. Higher VPD generally increases transpiration; lower VPD reduces it and can slow nutrient movement.
2) Use leaf temperature for better accuracy
Air temperature can differ from leaf temperature due to light intensity, airflow, and irrigation. A 1–2 °C leaf-to-air difference can noticeably shift VPD. If you measure leaf temperature, choose the leaf option; otherwise, use the offset mode to estimate leaf temperature from air readings.
3) Interpret targets by growth stage
The stage selector provides quick ranges used in many controlled gardens: 0.40–0.80 kPa for seedlings/clones, 0.80–1.20 kPa for vegetative growth, 1.00–1.30 kPa for early flower, and 1.20–1.60 kPa for late flower. Treat these as a starting point; adjust for your crop and airflow.
4) Diagnose low vs high VPD quickly
When the result is Low, the air is close to saturated—consider lowering humidity, increasing temperature slightly, or improving air exchange. When the result is High, the air is too dry—raise humidity, reduce temperature, or ease canopy-level airflow that strips moisture.
5) Build reliable logs and decisions
Record temperature basis, RH, and VPD at consistent times (lights-on, peak heat, and lights-off). Use the built-in CSV and PDF exports to keep a simple climate history. Pair VPD trends with irrigation notes to identify whether plant stress is driven by air conditions or root-zone limits.
FAQs
1) What unit is VPD reported in?
This calculator reports VPD in kilopascals (kPa). The same unit is used for SVP and AVP, making the values directly comparable and easy to log.
2) Should I use air temperature or leaf temperature?
Leaf temperature is usually more representative of plant response. If you can measure it, use leaf mode. If not, air mode is fine, or use offset mode to approximate leaf temperature.
3) Why does VPD change when humidity stays the same?
SVP rises as temperature increases. With the same relative humidity, warmer air can hold more moisture, so the deficit between SVP and AVP grows and VPD increases.
4) What does a “Low” status usually indicate?
Low VPD suggests air is too humid or too cool for the selected stage. Plants may transpire less, and moisture can linger on leaves, increasing disease risk in poorly ventilated spaces.
5) What does a “High” status usually indicate?
High VPD means air is too dry or too warm. Plants can transpire aggressively and may wilt if roots cannot keep up. Consider raising humidity or lowering temperature gradually.
6) Are the stage targets universal for every plant?
No. The ranges are general guidance for many controlled gardens. Different crops, cultivars, lighting, and airflow can shift ideal targets. Use the range as a baseline and tune using plant feedback.
7) How often should I recalculate VPD?
Check at least daily, and whenever you change ventilation, heating, humidification, or lighting. Many growers log morning and peak-heat readings to capture typical low and high VPD conditions.