VPD Calculator & VPD Chart

What VPD tells you

VPD (Vapor Pressure Deficit) is how much more water the air can still hold before it is saturated. It is the real driver of transpiration, stomatal opening, and calcium transport, so it sits behind everything from growth rate to blossom end rot. Too low and the air nears saturation, inviting condensation and fungal disease. Too high and the crop closes its stomata and stops growing.

How this VPD calculator works

The calculator uses the Tetens equation for saturation vapor pressure and reports two numbers. Air VPD uses air temperature only. Leaf VPD uses leaf temperature, which is what the plant actually experiences. A leaf in full radiation can sit several degrees away from air temperature, so leaf VPD is the value worth steering on. Set the leaf offset to match your crop, or measure leaf temperature directly with the Sigrow Stomata Camera.

VPD chart: the ranges to steer by

These are the bands shaded on the gauge and the VPD chart above, the working range from the Plant Empowerment approach for most fruiting vegetables. Younger crops prefer the lower end, so use the growth-stage selector to shift the target.

• Below 0.3 kPa: too low. Air near saturation, with condensation and Botrytis risk.
• 0.3 to 0.6 kPa: comfort zone, good for young plants and propagation.
• 0.6 to 1.2 kPa: optimal for most fruiting vegetables, with strong transpiration and CO2 uptake.
• 1.2 to 1.5 kPa: the high end. Watch for stress in sensitive varieties.
• Above 1.5 kPa: too high. Stomata close, photosynthesis stalls, and calcium transport drops.

How to measure VPD in your greenhouse

A calculator and a VPD chart describe one set of conditions. A real greenhouse has many: the aisle, the crop head, under a screen. The Sigrow Pixel measures VPD continuously at crop level, and the Stomata Camera reads leaf temperature and true leaf VPD from the plant itself. That is the difference between calculating VPD and steering on it. For the full picture, read VPD in the greenhouse: what it is and how to steer it.

Frequently asked questions

What is a good VPD? For most fruiting vegetables, aim for 0.6 to 1.2 kPa during the day. Young plants and propagation prefer the lower end, around 0.3 to 0.6 kPa.

What is the difference between air VPD and leaf VPD? Air VPD uses air temperature. Leaf VPD uses leaf temperature, which can differ by several degrees, so it reflects what the plant feels. Leaf VPD is the better value to steer on.

How do you lower or raise VPD? Lower VPD by adding humidity or reducing the leaf to air temperature gap. Raise it with venting, air movement, or heating. Screens and dosing both shift it.