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Psychrometric calculator
Find the moist-air state from dry-bulb temperature, one moisture property, and station pressure. Calculate in IP or SI units with a visible pressure basis.
Air-state inputs
Inputs are sent to VentilatePro to calculate and appear in the page URL. Shared links contain the inputs. No project data or account is needed.
Moist-air properties
Example resultPressure basis: Standard atmosphere at 0 ft.
Method: PsychroLib 2.5.0 · IP units.
Entered inputs: Dry-bulb temperature: 75.0 °F; Relative humidity: 50.0 %; Standard-atmosphere elevation: 0.0 ft.
Reproduce: https://ventilatepro.com/tools/psychrometric-calculator/?units=ip&dry_bulb=75&moisture_property=relative_humidity&moisture_value=50&pressure_source=elevation&elevation=0
| Property | Value | Unit |
|---|---|---|
| Dry-bulb temperature | 75.00 | °F |
| Wet-bulb temperature | 62.55 | °F |
| Dew-point temperature | 55.12 | °F |
| Relative humidity | 50.00 | % |
| Humidity ratio | 0.009236 | lb water/lb dry air |
| Moisture per unit dry air | 64.65 | grains/lb dry air |
| Specific enthalpy | 28.107 | Btu/lb dry air |
| Specific volume | 13.6792 | ft³/lb dry air |
| Moist-air density | 0.07378 | lb/ft³ |
| Station pressure | 14.6960 | psia |
| Water-vapor pressure | 0.21504 | psia |
| Degree of saturation | 49.26 | % |
CSV exports the displayed engineering units with unrounded values. JSON preserves the calculation engine’s native units; SI enthalpy is J/kg in JSON and kJ/kg in this table.
Calculation basis and limits
PsychroLib implements moist-air relationships from the ASHRAE Handbook—Fundamentals. The selected pressure applies to every calculated property. Standard-atmosphere pressure is an elevation-based estimate, not a live weather observation. A known absolute station pressure replaces the elevation estimate.
The humidity ratio is water mass per dry-air mass; specific volume and enthalpy also use a dry-air basis. Density includes both dry air and water vapor. IP and SI enthalpy conventions use different reference offsets, so compare enthalpy differences within one unit system.
This tool accepts dry-bulb temperatures from −40 to 212 °F (−40 to 100 °C), elevations from −1,500 to 30,000 ft, and known pressures from 10,000 to 120,000 Pa. It checks moisture inputs for physical consistency. Exactly dry air has no finite dew point and is outside this calculator’s input range. PsychroLib applies a minimum humidity ratio of 10⁻⁷ near the dry-air limit.
A single air state does not determine coil capacity, airflow, apparatus dew point, or bypass factor. Verify design inputs and project requirements before equipment selection. See the PsychroLib equation and API reference and VentilatePro calculation documentation.
See what changes at altitude
Compare 75 °F and 50% relative humidity at sea level and 5,000 ft. The worked example follows pressure, humidity ratio, enthalpy, and specific volume, with links that load both cases into this calculator.
Read the altitude worked example →Use the result in your HVAC workflow
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