VPD and Dew Point Calculator
Every figure in a day or night setpoint table comes from one equation and two choices. Enter your own numbers to build the same tables for your room. For why the day is steered by VPD and the night by dew point, read VPD by day, dew point by night.
Day: humidity from a VPD target
Pick a canopy temperature and a leaf VPD. The humidity that hits it comes out below.
Relative humidity
Night: humidity from a dew point margin
Pick a night temperature and how far below it you want to hold the dew point. We run 15 °F (8 °C).
Dew point setpoint
Implied relative humidity
Surface check: dew point of a room you have
Enter what your meter reads, then the coldest surface you can measure. Condensation forms wherever a surface sits at or below the dew point.
Dew point
The math is the Magnus equation for saturation vapor pressure, run entirely in your browser. Temperatures are entered in Fahrenheit and shown in both units. Nothing you type leaves the page.