Work out psychrometric properties instantly with clear inputs, formula shown and shareable results.
Moist air properties all follow from saturation vapour pressure, here from the Magnus relation. Relative humidity scales it to actual vapour pressure, the humidity ratio comes from the 0.62198 mass ratio of water to dry air, and enthalpy combines the sensible term 0.24 x T with the latent term of the water vapour carried.
Saturation pressure
Pws = 0.61094 x exp(17.625 Tc / (Tc + 243.04)) kPa
Humidity ratio and enthalpy
W = 0.62198 Pw / (P - Pw); h = 0.24 T + W (1061 + 0.444 T)
Pws = 0.61094 x exp(17.625 Tc / (Tc + 243.04)) kPa. Moist air properties all follow from saturation vapour pressure, here from the Magnus relation.
Seven thousand grains make a pound, and HVAC coil selection tables are written in grains per pound of dry air because the numbers are easier to compare than four-decimal fractions.
This calculator takes 3 inputs: Dry bulb temperature, Relative humidity, Barometric pressure. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.