Psychrometric Calculator
Plan your hvac project with our free psychrometric calculator. Get precise measurements, material lists, and budgets.
Formula
W = 0.62198 * Pw / (P - Pw) where Pw = (RH/100) * Pws
Where W is humidity ratio (kg/kg), Pw is partial vapor pressure, Pws is saturation vapor pressure from the Antoine equation, P is atmospheric pressure, and RH is relative humidity percentage.
Frequently Asked Questions
What is enthalpy in psychrometric calculations and how is it used?
Enthalpy in psychrometric calculations represents the total heat content of moist air per kilogram of dry air, measured in kilojoules per kilogram. It includes both the sensible heat (related to temperature) and the latent heat (related to moisture content). The formula combines the dry air component (approximately 1.006 times the dry bulb temperature) with the water vapor component (humidity ratio multiplied by the sum of the latent heat of vaporization at zero degrees and the specific heat of steam times the temperature). HVAC engineers use enthalpy to calculate cooling and heating loads, design air handling units, and determine the energy required for various air conditioning processes such as heating, cooling, humidification, and dehumidification.
How does atmospheric pressure affect psychrometric calculations?
Atmospheric pressure significantly affects all psychrometric properties because it changes the density of air and the behavior of water vapor within it. At higher altitudes where pressure is lower, the saturation vapor pressure remains the same (it depends only on temperature), but the humidity ratio for a given relative humidity increases because there is less dry air per unit volume. This means air conditioning equipment at high altitudes must handle more moisture per unit mass of dry air. Standard psychrometric charts are drawn for sea-level pressure of 101.325 kPa, but engineers working at different altitudes must use corrected charts or calculations. A 1000-meter increase in elevation reduces atmospheric pressure by roughly 12%, which noticeably changes enthalpy and humidity ratio values.
How accurate are the results from Psychrometric Calculator?
All calculations use established mathematical formulas and are performed with high-precision arithmetic. Results are accurate to the precision shown. For critical decisions in finance, medicine, or engineering, always verify results with a qualified professional.
Can I use Psychrometric Calculator on a mobile device?
Yes. All calculators on NovaCalculator are fully responsive and work on smartphones, tablets, and desktops. The layout adapts automatically to your screen size.
What formula does Psychrometric Calculator use?
The formula used is described in the Formula section on this page. It is based on widely accepted standards in the relevant field. If you need a specific reference or citation, the References section provides links to authoritative sources.
How do I get the most accurate result?
Enter values as precisely as possible using the correct units for each field. Check that you have selected the right unit (e.g. kilograms vs pounds, meters vs feet) before calculating. Rounding inputs early can reduce output precision.