VPD Calculator

What it does

A VPD and humidity deficit calculator that computes air vapor pressure deficit, humidity deficit and dew point from temperature and relative humidity. It also finds the RH that gives a 1.0 kPa VPD at the current temperature.

When to use it

Use it to check a temperature and RH setpoint against a VPD target and see which RH hits that target from 18 to 30 °C. An optional tomato mode adds plant morphology inputs for a plant health report.

How it calculates

• Saturation vapor pressure from the Magnus-Tetens equation: es = 0.61094·exp(17.625·T ÷ (243.04 + T))
• Dew point from the inverse Magnus-Tetens equation, using actual vapor pressure
• Absolute humidity = 216.7 × e (hPa) ÷ T (K). Humidity deficit = saturation minus actual absolute humidity.
• Target RH is found by binary search for the RH that gives a 1.0 kPa VPD. VPD outside 0.6 to 1.4 kPa is flagged.

What you enter

Temperature(°C or °F)

Relative Humidity(%)

CO₂ Level(ppm)

Light Intensity(μmol/m²/s)

Air Movement(m/s, tomato mode)

Head Width(mm, tomato mode)

Stem Diameter(mm, tomato mode)

Internode Length(cm, tomato mode)

Truss Angle(degrees, tomato mode)

Leaf Angle(degrees, tomato mode)

What you get

VPD(kPa)

Humidity Deficit(g/m³)

Dew Point(°C or °F)

Target RH(%)

VPD Target Chart: Optimal RH by Temperature(%)

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