VPD Calculator — Optimize Greenhouse Climate Instantly

Calculate vapor pressure deficit from air temperature, leaf temperature, and relative humidity. Free online VPD calculator with step-by-step formula breakdown, plant-stage interpretation, and copy & share support for precision horticulture.

Verified Formula Instant Results Privacy First

VPD Calculator

Enter temperature and humidity readings to calculate the vapor pressure deficit for your growing environment.

Enter readings and click Calculate VPD to see the result.

VPD Formula Explained

The vapor pressure deficit is the difference between the saturation vapor pressure and the actual vapor pressure of the air. It quantifies the atmospheric demand for water from plant leaves.

SVP = 0.61078 × exp(17.27 × T / (T + 237.3))
AVP = SVP × (RH / 100)
VPD = SVP − AVP = SVP × (1 − RH/100)

Variable Definitions

  • SVP — Saturation Vapor Pressure (kPa): the maximum water vapor air can hold at temperature T
  • AVP — Actual Vapor Pressure (kPa): the current water vapor content of the air
  • T — Temperature in degrees Celsius (°C)
  • RH — Relative Humidity as a percentage (0–100%)
  • VPD — Vapor Pressure Deficit (kPa): the driving force for plant transpiration

For leaf VPD, the leaf temperature replaces air temperature in the SVP formula, while AVP is still derived from air temperature and RH. This accounts for the temperature difference between the leaf surface and surrounding air.

How to Calculate Vapor Pressure Deficit

Calculating VPD involves three clear steps. Follow this process for accurate greenhouse climate management:

  1. Calculate SVP — Use the Tetens equation: SVP = 0.61078 × exp(17.27 × T / (T + 237.3)) where T is air temperature in Celsius.
  2. Calculate AVP — Multiply SVP by relative humidity divided by 100: AVP = SVP × (RH/100).
  3. Compute VPD — Subtract AVP from SVP: VPD = SVP − AVP. The result is in kilopascals (kPa).

For leaf VPD, repeat step 1 using leaf temperature instead of air temperature to get SVPleaf, then use the same AVP from step 2 to compute Leaf VPD = SVPleaf − AVP.

VPD Calculator Examples

Example 1: Basic Greenhouse VPD

Air temperature 25°C, relative humidity 60%.

SVP = 0.61078 × exp(17.27 × 25 / (25 + 237.3)) = 3.169 kPa
AVP = 3.169 × 0.60 = 1.901 kPa
VPD = 3.169 − 1.901 = 1.268 kPa

Interpretation: Ideal for flowering and fruiting stages (1.2–1.6 kPa range).

Example 2: High Humidity Warning

Air temperature 22°C, relative humidity 85%.

SVP = 0.61078 × exp(17.27 × 22 / (22 + 237.3)) = 2.645 kPa
AVP = 2.645 × 0.85 = 2.248 kPa
VPD = 2.645 − 2.248 = 0.397 kPa

Interpretation: Too low — risk of fungal disease and poor transpiration. Increase ventilation or reduce humidity.

Example 3: Leaf VPD With Temperature Offset

Air temperature 28°C, leaf temperature 26°C, relative humidity 55%.

SVPair = 0.61078 × exp(17.27 × 28 / (28 + 237.3)) = 3.780 kPa
SVPleaf = 0.61078 × exp(17.27 × 26 / (26 + 237.3)) = 3.361 kPa
AVP = 3.780 × 0.55 = 2.079 kPa
Leaf VPD = 3.361 − 2.079 = 1.282 kPa

Real-World VPD Applications in Agriculture

  • Greenhouse Climate Control: Adjusting ventilation, heating, and fogging systems to maintain target VPD ranges for optimal plant transpiration.
  • Indoor Vertical Farming: Managing HVAC and humidification in controlled environment agriculture for consistent crop quality.
  • Cannabis Cultivation: Precise VPD management throughout vegetative and flowering phases to maximize yield and terpene production.
  • Seedling Propagation: Maintaining low VPD (0.4–0.8 kPa) in propagation domes to prevent desiccation of young cuttings.
  • Disease Prevention: Avoiding prolonged low VPD conditions that favor powdery mildew, botrytis, and other fungal pathogens.
  • Irrigation Scheduling: Using VPD trends to anticipate plant water demand and optimize irrigation timing.
  • Post-Harvest Storage: Controlling VPD in storage environments to minimize moisture loss from harvested produce.

People Also Ask

VPD stands for Vapor Pressure Deficit. It measures the difference between the amount of moisture in the air and how much moisture the air can hold when saturated at a given temperature. In agriculture, VPD helps growers manage plant transpiration rates and optimize greenhouse climate for healthier growth.
VPD is calculated by first determining Saturation Vapor Pressure (SVP) using SVP = 0.61078 × exp(17.27 × T / (T + 237.3)), then calculating Actual Vapor Pressure (AVP) = SVP × (RH/100), and finally VPD = SVP - AVP. The result is measured in kilopascals (kPa).
Ideal VPD ranges vary by growth stage: 0.4–0.8 kPa for propagation and seedlings, 0.8–1.2 kPa for vegetative growth, and 1.2–1.6 kPa for flowering and fruiting. VPD below 0.4 kPa may promote disease, while values above 1.6 kPa can cause plant stress.
Air VPD uses air temperature for SVP calculation, while leaf VPD uses actual leaf surface temperature. Leaf temperature can differ from air temperature due to transpiration cooling or radiant heating, making leaf VPD a more accurate measure of the water vapor gradient at the stomatal level.
VPD directly influences plant transpiration rates, nutrient uptake, and stomatal opening. Maintaining optimal VPD in greenhouses helps prevent issues like powdery mildew from high humidity, leaf scorch from excessive transpiration, and calcium deficiencies caused by low transpiration rates.

Frequently Asked Questions

Yes. Toggle to Leaf VPD mode to enter air temperature, leaf temperature, and relative humidity. The calculator uses leaf temperature for the saturation vapor pressure at the leaf surface, providing a more accurate VPD measurement for stomatal-level analysis.
The calculator uses degrees Celsius (°C) for temperature, percentage (%) for relative humidity, and outputs vapor pressure deficit in kilopascals (kPa). These are the standard units used in greenhouse management and horticultural science worldwide.
VPD above 1.6 kPa typically indicates high atmospheric demand that can cause stomatal closure and plant stress. VPD below 0.4 kPa indicates very low demand, which can lead to poor transpiration, reduced nutrient uptake, and increased risk of fungal diseases.
VPD should be monitored continuously if possible, as it fluctuates throughout the day with changes in temperature and humidity. At minimum, check VPD during key transition periods: early morning, midday when temperatures peak, and late afternoon as conditions change.
This calculator accepts Celsius only, as the Tetens equation is calibrated for Celsius. To convert Fahrenheit to Celsius, subtract 32 and multiply by 5/9. For example, 77°F = (77 - 32) × 5/9 = 25°C.
The Tetens equation (SVP = 0.61078 × exp(17.27 × T / (T + 237.3))) is a widely accepted empirical formula for calculating saturation vapor pressure over water. It is accurate within approximately 0.1% for temperatures between 0°C and 50°C, making it ideal for greenhouse and agricultural applications.

VPD & Horticulture Glossary

Vapor Pressure Deficit

The difference between saturation vapor pressure and actual vapor pressure, measured in kPa. Drives plant transpiration.

Saturation Vapor Pressure

The maximum partial pressure of water vapor in air at a given temperature before condensation begins.

Actual Vapor Pressure

The current partial pressure exerted by water vapor in the air, calculated as SVP multiplied by relative humidity.

Transpiration

The process by which plants lose water vapor through stomatal pores in their leaves, driven by VPD.

Stomatal Conductance

The rate at which stomata open to allow gas exchange. High VPD can cause stomatal closure to conserve water.

Tetens Equation

An empirical formula for calculating saturation vapor pressure from temperature, accurate for agricultural temperature ranges.

Leaf Boundary Layer

The thin layer of still air surrounding a leaf surface that affects heat and vapor transfer between the leaf and ambient air.

kPa (Kilopascal)

A unit of pressure equal to 1,000 pascals. VPD is typically expressed in kPa in horticultural and greenhouse applications.

Editorial Review & Methodology

This VPD calculator was built and reviewed by the NumbrWiz Editorial Team. The vapor pressure deficit formula using the Tetens equation is a widely accepted standard in horticultural science, validated against peer-reviewed literature including the FAO Irrigation and Drainage Paper No. 56 and contemporary greenhouse climate management research.

  • Formula verification: Cross-checked against the Tetens equation as published in agricultural and meteorological standards.
  • Edge case testing: Tested with extreme humidity values (0–100%), freezing to high temperatures, and leaf temperature offsets.
  • Practical validation: Results compared against commercial greenhouse environmental controllers and published VPD charts.

Transparency note: All calculations run client-side in your browser. No data is ever collected, stored, or transmitted. VPD results are for educational and planning purposes; always cross-reference with calibrated environmental sensors for critical growing decisions.

Page last reviewed: May 2026 · NumbrWiz Editorial Team