Vapor Pressure Deficit (VPD) Calculator

This article and the video below provide a demonstration of Adicot's Vapor Pressure Deficit (VPD) Calculator for Indoor Growers and Grow Rooms. This calculator is a useful tool for Indoor Growers setting up Grow Rooms. The user is able to hone in on temperature and humidity values to optimize plant health as well as energy conservation.

The video shows the earlier version of the calculator. The current one works the same way, and its results update as you type.

This Vapor Pressure Deficit (VPD) calculator is used to determine temperature and humidity for indoor grow rooms. I am not a grower, so I cannot advise you what your VPD should be, but here is an excellent article from Cannabis Science and Technology describing VPD at different stages of growth.

So let us get right into it. You can choose either US or metric units. For this demonstration, I will use US units. Begin by entering room conditions of 78 degrees Fahrenheit and 60% relative humidity. The leaf temperature is optional: as a leaf transpires, evaporative cooling keeps it below the room temperature. If you do not know your leaf temperature, a rule of thumb is that you could assume a temperature drop of about 2 degrees Fahrenheit. Following that rule of thumb, we will use a leaf temperature of 76 degrees Fahrenheit. These inputs give a room VPD of 1.31 kPa and a leaf VPD of 1.1 kPa.

The clear benefit of targeting a VPD is healthy, robust plants. Another benefit of targeting VPD is energy savings. Let us try one more scenario. Let us say you are in a hot, humid climate. You can allow the temperature to be set to 82 degrees Fahrenheit and 65% relative humidity and still achieve the same leaf and room VPD values of 1.31 kPa and 1.1 kPa, respectively.