What is vapor pressure deficit (VPD)?

VPD is the difference between the amount of moisture the air can hold when saturated and the amount it actually holds. It's calculated from temperature and relative humidity. Higher VPD means drier air, which increases evaporation and plant water loss.

How do I use this calculator?

Enter the air temperature in degrees Celsius and the relative humidity in percent. The calculator will compute the saturation vapor pressure and the vapor pressure deficit. Use these values to assess environmental conditions for plants or other applications.

Why is VPD important for plants?

VPD influences transpiration and stomatal behavior. Moderate VPD (around 0.8-1.2 kPa) is often ideal for many crops. Too high VPD can cause plant stress and reduced growth, while too low VPD can hinder nutrient uptake and increase disease risk.

Biology & Life Science

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Vapor Pressure Deficit Calculator.

Calculate saturation vapor pressure and vapor pressure deficit from temperature and relative humidity.

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02 / ANSWER

Air temperature

Relative humidity

Saturation vapor pressure

3.1678

Actual vapor pressure

1.9007

Vapor pressure deficit

1.2671

Educational psychrometric calculation using the Magnus saturation-vapor-pressure approximation. It does not prescribe crop, greenhouse, or health actions.

FAQs

What does VPD mean?

Vapor pressure deficit is the difference between saturation vapor pressure and actual vapor pressure at a given temperature and relative humidity.

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Cite this calculator

Canonical URL: https://mathify.one/en/biology/vapor-pressure-deficit

Cite as: Mathify. (n.d.). Vapor Pressure Deficit Calculator. https://mathify.one/en/biology/vapor-pressure-deficit

Use Cases

Greenhouse climate management

Monitor VPD to optimize humidity and temperature for plant growth, preventing stress and disease.

Example: A grower adjusts ventilation to keep VPD between 0.8 and 1.2 kPa for tomatoes.

Agricultural irrigation scheduling

Estimate water loss from crops to plan irrigation more accurately.

Example: A farmer uses VPD to decide when to irrigate a vineyard.

Frequently Asked Questions

What is vapor pressure deficit (VPD)?: VPD is the difference between the amount of moisture the air can hold when saturated and the amount it actually holds. It's calculated from temperature and relative humidity. Higher VPD means drier air, which increases evaporation and plant water loss.
How do I use this calculator?: Enter the air temperature in degrees Celsius and the relative humidity in percent. The calculator will compute the saturation vapor pressure and the vapor pressure deficit. Use these values to assess environmental conditions for plants or other applications.
Why is VPD important for plants?: VPD influences transpiration and stomatal behavior. Moderate VPD (around 0.8-1.2 kPa) is often ideal for many crops. Too high VPD can cause plant stress and reduced growth, while too low VPD can hinder nutrient uptake and increase disease risk.

Tips & Common Mistakes

Tips

Ensure temperature is in Celsius and humidity is in percent for accurate results.
Use a reliable hygrometer and thermometer to get precise readings.
Check VPD at different times of day, as it fluctuates with temperature and humidity.
Compare VPD values with known optimal ranges for your specific plants.

Common Mistakes to Avoid

Entering relative humidity as a decimal (e.g., 0.5) instead of a percentage (50).
Using Fahrenheit instead of Celsius without converting.
Ignoring that VPD changes with temperature even if humidity stays the same.

Last updated: August 13, 2026