Psychrometric Calculator

Psychrometrics is the study of thermodynamic properties of moist air. Engineers use these relationships to design heating, ventilation, and air-conditioning systems, evaluate drying processes, assess indoor comfort, and interpret weather observations. This psychrometric calculator starts with dry-bulb temperature, relative humidity, and atmospheric pressure, then estimates dew point, wet-bulb temperature, humidity ratio, and moist-air enthalpy. Dry-bulb temperature is the ordinary air temperature measured by a shielded thermometer. Relative humidity compares the actual water-vapor pressure with saturation vapor pressure at that temperature. It is therefore temperature dependent: warming air without adding moisture lowers relative humidity, while cooling it raises relative humidity. At one hundred percent relative humidity, the air is saturated and dry-bulb, dew-point, and wet-bulb temperatures converge. Dew point is the temperature to which air must be cooled at constant pressure and moisture content to reach saturation. This calculator estimates saturation vapor pressure with a Magnus relationship and analytically inverts that relationship for dew point. Surfaces below dew point can collect condensation, which matters for windows, ducts, insulation, cold pipes, building envelopes, and industrial equipment. Humidity ratio is the mass of water vapor per mass of dry air. Unlike relative humidity, it directly represents moisture content. The calculator derives it from water-vapor partial pressure and total atmospheric pressure, then displays grams of vapor per kilogram of dry air. Pressure matters because the same vapor pressure produces a different mass ratio at high elevation. Moist-air enthalpy combines sensible heat of dry air with latent and sensible energy carried by water vapor, making it useful for cooling-coil, heating, humidification, and dehumidification energy balances. Wet-bulb temperature approximates the equilibrium temperature reached by evaporative cooling. The displayed value uses a widely used empirical approximation based on dry-bulb temperature and relative humidity. It is accurate for ordinary environmental conditions but is not a full iterative thermodynamic solution and does not explicitly include pressure. Close engineering design work, extreme temperatures, very low humidity, or unusual pressure should use an accepted psychrometric standard or property library. All outputs assume the entered values describe a uniform, steady air sample. Sensor calibration, radiant heating, poor airflow, and pressure errors can materially affect measured conditions. Use this calculator for education, preliminary HVAC checks, and quick comparisons, then verify safety-critical or specification-grade decisions with calibrated instruments and applicable engineering standards.