Moist-air properties from any two known conditions. Uses the ASHRAE Hyland-Wexler saturation formulation — correct over both water and ice — with the Buck enhancement factor and true elevation correction.
Sea level = 0. Denver ≈ 5,280 ft. Elevation changes humidity ratio and wet-bulb materially — most free calculators ignore it.
Air properties
Psychrometric chart
Curves are lines of constant relative humidity at your working pressure. The marker is your state point.
Methodology — and why this differs from other free calculators
Saturation pressure: ASHRAE Fundamentals Hyland-Wexler correlation, using the separate formulation over ice below 0 °C and over liquid water above it. Calculators built on the Antoine equation drift near and below freezing — exactly the range that matters for condensation, freeze protection and low-temperature coils.
Enhancement factor: moist air is not an ideal mixture — the effective saturation pressure of water vapour in air sits about 0.4 % above that over a pure water surface. We apply the Buck enhancement factor, with separate forms over water and over ice. Omitting it understates humidity ratio by roughly 0.3–0.6 %, which is the single most common discrepancy between free calculators and commercial reference software.
Dew point: found by numerically inverting the same effective saturation curve, so it is consistent with the rest of the state rather than fitted from a separate polynomial.
Wet-bulb: solved iteratively from the adiabatic saturation relationship, with the correct sub-freezing form applied below 0 °C.
Enthalpy: computed in the native unit system. IP uses the 0 °F datum h = 0.240·T + W(1061 + 0.444·T); SI uses the 0 °C datum. Converting one to the other by a unit factor alone is wrong by roughly 8 Btu/lb at room conditions — a common error.
Pressure: true barometric pressure from the standard atmosphere, P = 101.325(1 - 2.25577×10-5Z)5.2559 kPa. Not assumed to be sea level.
Verified against ASHRAE tabulated values at 24 °C / 50 % RH: saturation pressure 2985.1 Pa, dew point 12.95 °C, wet-bulb 17.07 °C, enthalpy 47.81 kJ/kg.
Independently validated against commercial psychrometric software across 12 conditions spanning −18 to 54 °C (0–130 °F), 10–100 % RH, including sub-freezing and exactly saturated states — 60 property comparisons, all within tolerance.