HVAC · Moist air · Psychrometrics
Psychrometric Calculator — Dew Point, Wet Bulb, Humidity & Enthalpy
Resolve a moist-air state from dry-bulb temperature plus relative humidity, dew point or wet-bulb temperature. Calculate humidity ratio, enthalpy, specific volume, density, vapour pressure and condensation margin with altitude-aware pressure.
Altitude automatically adjusts standard atmospheric pressure. Sea level = 101.325 kPa.
How to use it
Pick the pair you actually know. Enter dry-bulb temperature and RH for room or weather data; use dew point for condensation work; use wet bulb for HVAC field readings. Adjust altitude when you are not near sea level. Every dependent property updates from the same air state.
What the results tell you
Humidity ratio measures water vapour per kilogram of dry air. Enthalpy combines sensible and latent energy. Dew point is the surface-temperature threshold for condensation. Specific volume and density help convert air mass flow to volumetric flow.
Formula and limits
Pv=RH·Pws(Tdb); W=0.621945·Pv/(P−Pv); h=1.006Tdb+W(2501+1.86Tdb); v=0.287042(Tdb+273.15)(1+1.607858W)/P.
- Moist air is treated as an ideal-gas mixture at the entered barometric pressure.
- Saturation pressure uses a Magnus-type correlation suitable for ordinary HVAC screening; critical design should be checked against the applicable ASHRAE/CIBSE method.
- Wet-bulb values are solved numerically from the moist-air enthalpy relation and are intended for engineering screening, not calibration work.
FAQs
What inputs can this psychrometric calculator use?
Choose dry bulb plus relative humidity, dry bulb plus dew point, or dry bulb plus wet bulb. The calculator resolves the remaining moist-air properties from that state.
Does altitude affect psychrometric calculations?
Yes. Altitude changes barometric pressure, which changes humidity ratio, specific volume and related properties. You can enter altitude and the calculator estimates standard-atmosphere pressure.
What does condensation margin mean?
It is dry-bulb temperature minus dew-point temperature. A surface at or below the dew point can collect condensation when exposed to that air.
Can I use this instead of a psychrometric chart?
It is useful for quick state-point calculations and cross-checks. A full chart remains valuable for visualising HVAC processes such as cooling, dehumidification, mixing and humidification.