Engineering tools · Free to use

Psychrometric Calculator

Moist Air Properties

Estimate moist-air properties from dry-bulb temperature, relative humidity and absolute pressure.

Input parameters

Inputs and calculations stay in this browser.

Results

Humidity ratio— g/kg dry air

Specific enthalpy— kJ/kg dry air

Dew / frost-point temperature— °C

Wet-bulb temperature— °C

Specific volume— m³/kg dry air

Enthalpy uses the model's reference state; humidity ratio, enthalpy and specific volume are per unit mass of dry air.

How to use

Enter absolute pressure, not gauge pressure. Input relative humidity uses the saturation vapour pressure at the dry-bulb temperature: over ice at or below 0.01 °C, and over liquid water above 0.01 °C. Relative humidity measured with respect to supercooled liquid water cannot be entered directly as an ice-based value. A reported dew / frost point at or below 0.01 °C is calculated using ice saturation and should be interpreted as a frost point; above 0.01 °C it is a liquid-water dew point. Recalculate after changing an input.

Applicability

Approximate engineering estimates within the stated input ranges.
Uses an approximate moist-air model; supercooled droplets, supersaturation, condensation and frost formation are not simulated.
The wet-bulb calculation switches between water and ice branches at 0 °C, distinct from the 0.01 °C saturation-pressure triple-point switch. Near freezing, phase assumptions and models can differ substantially; displayed digits do not imply accuracy. For critical conditions and equipment design, consult applicable standards and more detailed property models.

Software license

Worked example

At 25 °C dry-bulb temperature, 50% relative humidity and 101.325 kPa absolute pressure, PsychroLib gives approximately 9.881 g/kg dry air humidity ratio, 50.322 kJ/kg dry air enthalpy, 13.864 °C dew point, 17.889 °C wet bulb and 0.85804 m³/kg dry air specific volume. Enthalpy uses the model reference state.

For engineering estimates; check the operating conditions and applicable requirements for design.