Psychrometric Calculator
Humidity ratio, enthalpy, saturation pressure and density of moist air at a given state.
Results
Humidity ratio
0.009277
kg/kg
Humidity ratio
9.277
g/kg
Enthalpy
47.7592
kJ/kg
Vapour pressure
2.97807
kPa
Density
1.17042
kg/m³
What this tool does
Enthalpy is the number air conditioning is designed around, because cooling has to remove both the temperature and the moisture, and only enthalpy counts both. That is why dehumidifying costs so much: at 24 °C and 50 % relative humidity, over half the enthalpy of the air is latent heat carried by the water vapour, not sensible heat you can feel on a thermometer.
Formula
W = 0.621 98 pw ÷ (p − pw) ; h = 1.006 t + W(2501 + 1.86 t)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
tt | Temperature | °C |
rh | Relative humidity | % |
pp | Atmospheric pressure | kPa |
WW | Humidity ratio | kg/kg |
GK | Humidity ratio | g/kg |
HH | Enthalpy | kJ/kg |
PS | Vapour pressure | kPa |
DE | Density | kg/m³ |
Worked example
- Temperature24 °C
- Relative humidity50 %
- Atmospheric pressure101.325 kPa
- Humidity ratio0.009277 kg/kg
- Humidity ratio9.277 g/kg
- Enthalpy47.7592 kJ/kg
- Vapour pressure2.97807 kPa
- Density1.17042 kg/m³
Limitations
- For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.