Psychrometric Properties (Humidity Ratio / Enthalpy / RH)
Compute the full set of moist-air (psychrometric) state properties from dry-bulb temperature plus one humidity input (relative humidity φ, wet-bulb temperature, dew-point temperature, or humidity ratio W). Returns humidity ratio W (kg/kg and g/kg), relative humidity φ (%), dew-point, wet-bulb, enthalpy h (kJ/kg dry air), specific volume v (m³/kg dry air), partial vapour pressure P_w, and saturation pressure P_ws. Uses the Magnus saturation-pressure fit; wet-bulb is solved iteratively from the thermodynamic psychrometric equation. Default standard atmosphere 101.325 kPa (adjustable). Temperature in °C/K/°F; all reported temperatures are in °C.
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Key facts
Category
Math & Numbers
Input types
number, select
Output type
json
Sample coverage
4
API ready
Yes
Overview
Calculate the complete psychrometric state of moist air from dry-bulb temperature and one humidity input: relative humidity, wet-bulb temperature, dew point, humidity ratio, enthalpy, specific volume, vapour pressure, and saturation pressure.
When to use
Convert a dry-bulb and relative-humidity reading into humidity ratio, dew point, wet-bulb temperature, and enthalpy.
Derive relative humidity and other moist-air properties from a known humidity ratio.
Check psychrometric conditions at standard or site-specific atmospheric pressure.
How it works
1Enter the dry-bulb temperature and select °C, K, or °F.
2Choose one known humidity input: relative humidity, wet-bulb temperature, dew-point temperature, or humidity ratio.
3Enter atmospheric pressure, or use the default 101.325 kPa, and select the humidity-ratio and pressure units.
4The calculator applies the Magnus saturation-pressure fit and iteratively solves wet-bulb temperature, returning the full state as JSON.
Use cases
HVAC design checks using temperature, humidity, pressure, enthalpy, and specific volume.
Indoor-air and environmental measurements that require dew-point or wet-bulb calculations.
Engineering and laboratory calculations involving moist-air mass and energy properties.
Examples
1. 25 °C air at 50% relative humidity
HVAC engineer
Background
An HVAC engineer needs the main moist-air properties for air at 25 °C and standard atmospheric pressure.
Problem
Convert the relative-humidity reading into humidity ratio, dew point, wet bulb, enthalpy, and specific volume.
How to use
Enter 25 as the dry-bulb temperature, select °C, choose Relative Humidity φ, and enter 50. Use 101.325 kPa pressure.
The result is approximately W=9.876 g/kg, φ=50%, dew point=13.86 °C, wet bulb=17.89 °C, enthalpy=50.31 kJ/kg dry air, and specific volume=0.8578 m³/kg dry air.
2. 20 °C air from a humidity ratio
Building analyst
Background
A building analyst has a humidity ratio of 7.6 g/kg dry air and wants the corresponding relative humidity and condensation-related temperatures.
Problem
Calculate relative humidity, dew point, wet-bulb temperature, and enthalpy from the measured humidity ratio.
How to use
FAQ
What inputs are required?
Enter a dry-bulb temperature and one humidity value. The humidity value can be relative humidity, wet-bulb temperature, dew-point temperature, or humidity ratio.
Which temperature units are supported?
Dry-bulb and humidity temperatures can be entered in °C, K, or °F. Reported temperatures are returned in °C.
What atmospheric pressure is used?
The default pressure is 101.325 kPa. You can replace it with a custom value in kPa or hPa.
What properties does the calculator return?
Results include humidity ratio, relative humidity, dew point, wet bulb, enthalpy, specific volume, partial vapour pressure, and saturation pressure.
Can humidity ratio be entered in g/kg?
Yes. Select g/kg dry air or kg/kg dry air for the humidity-ratio input and output.
The result is approximately W=7.6 g/kg, relative humidity=52.33%, dew point=9.94 °C, wet bulb=13.69 °C, enthalpy=39.43 kJ/kg dry air, and specific volume=0.8401 m³/kg dry air.