Psychrometric Calculator

• •Use the Psychrometric Calculator when solving homework or exam problems that require quick numerical verification of your hand calculations — instant feedback helps identify arithmetic errors before they propagate.
• •Use it during the early design phase to rapidly iterate on parameters and narrow down feasible configurations before committing time to detailed finite element simulations or full design packages.
• •Use it when reviewing a colleague's calculation or checking a vendor's data sheet for plausibility — a quick sanity check can prevent costly downstream errors.
• •Use it to generate reference data for a technical report or presentation without manual computation, ensuring consistent, reproducible numbers throughout the document.
• •Use it in the field when a quick estimate is needed and a full engineering software package is not available.

The Psychrometric Calculator is a precision engineering calculation tool designed for students, engineers, and technical professionals. Calculate humidity ratio, dew point, enthalpy, and specific volume from dry-bulb temperature and relative humidity All calculations are performed using established engineering formulas from the relevant scientific literature and standards. Inputs support both metric (SI) and imperial unit systems, with unit conversion handled automatically — simply select your preferred unit from the dropdown next to each field. Results are computed instantly in the browser without sending data to a server, ensuring both speed and privacy. This calculator is intended as a supplementary tool for learning and design exploration; always verify results against authoritative references for safety-critical applications.

Psychrometrics is the study of moist air — mixtures of dry air and water vapor. The key properties are: dry-bulb temperature (T_db, the air temperature from an ordinary thermometer), wet-bulb temperature (T_wb, the temperature of a water-wetted thermometer bulb that represents evaporative cooling), relative humidity (φ, the ratio of current vapor pressure to saturation vapor pressure at the same temperature), humidity ratio (W, mass of water vapor per unit mass of dry air), dew point (the temperature at which condensation begins when the air is cooled at constant pressure), enthalpy (h, total energy per unit mass of dry air), and specific volume (v). These properties are related through saturation curves and the psychrometric chart — a graphical representation that shows all properties simultaneously and allows any two to specify the complete state. For air-conditioning calculations, the enthalpy is particularly important because it captures both sensible heat (temperature change) and latent heat (moisture change) in a single value. Cooling and dehumidification moves air across the psychrometric chart from high h, high W to low h, low W — and the required refrigeration capacity equals the mass flow times the enthalpy difference. Common calculations include: sensible heating or cooling (constant W, varying T); evaporative cooling (constant enthalpy, crossing the saturation curve); humidification (adding moisture at constant T or following an adiabatic saturation line); and dehumidification (usually by cooling below dew point, then reheating). Building HVAC load calculations rely heavily on psychrometric analysis to determine cooling capacity, reheat, and humidity control requirements. The calculator implements the ASHRAE psychrometric formulas valid for atmospheric pressure (101.325 kPa) and temperatures from −50°C to 200°C.

• •HVAC cooling load analysis: compute required refrigeration capacity for space conditioning given outdoor air conditions and desired indoor conditions. The total load is mass flow × enthalpy difference from outdoor to indoor state.
• •Dehumidification sizing: determine how much moisture must be removed to reach a target humidity ratio. The calculator shows the required reheat after cooling below dew point to return temperature to comfort range.
• •Evaporative cooling effectiveness: given inlet dry-bulb and wet-bulb temperatures, compute the minimum temperature achievable by evaporative cooling (approaches wet-bulb asymptotically). Useful for swamp cooler sizing in dry climates.
• •Outdoor air calculations: for 100% outdoor air systems, compute the enthalpy and moisture content of fresh air at various design conditions to size cooling and heating coils properly.
• •Drying process design: compute the moisture-carrying capacity of heated air used to dry grain, lumber, laundry, or industrial products. The air's enthalpy and humidity determine how much water it can absorb before saturation.