How it's calculated
RH = e ÷ eₛ(T) × 100
eₛ(T) = 6.1094·exp(17.625·T/(243.04+T)) = saturation vapour pressure at air temperature T (°C); e = actual vapour pressure = eₛ(Td) at dew point Td. Magnus formula. VPD = eₛ − e.
Common questions
How does dew point relate to relative humidity?
When the dew point is close to the air temperature the humidity is high, and a larger gap between them means drier air.
What is VPD?
Vapor pressure deficit is the difference between how much moisture the air can hold and how much it holds now, and growers use it to judge plant transpiration.