Enter either the air temperature or the specific enthalpy into the calculator to estimate the specific enthalpy of dry air (referenced to 0°C).

Dry Air Enthalpy Calculator

Uses the approximation h ≈ 1.005·T (h in kJ/kg, T in °C relative to 0°C). For moist air, enthalpy depends on humidity.

Enter any 1 value to calculate the missing variable

Dry Air Enthalpy (Approximation) Formula

The following approximation is commonly used to estimate the specific enthalpy of dry air as a function of temperature (assuming a nearly constant specific heat at about atmospheric pressure, referenced to 0°C).

h \approx 1.005\,T
  • Where h is the specific enthalpy of dry air (kJ/kg), referenced to 0°C
  • T is the air temperature (°C)

To calculate dry air enthalpy with this approximation, multiply the temperature (°C) by 1.005 to get kJ/kg.

Air Enthalpy Definition

What is air enthalpy? Specific enthalpy is a thermodynamic property equal to internal energy plus flow work: h = u + pv. For air treated as an ideal gas, changes in specific enthalpy depend mainly on temperature (and for moist air, also on humidity).

Example Problem

How to calculate air enthalpy?

  1. First, determine the temperature of the air.

    For this example, the air mass has a temperature of 60 degrees Celsius.

  2. Next, determine the enthalpy.

    Using the approximation above (dry air, referenced to 0°C), calculate the specific enthalpy. h = 1.005 × 60 = 60.30 kJ/kg.

  3. Finally, convert into the necessary units.

    For this problem, we want to convert to J/kg, so we need to multiply the result by 1000. 60.30 kJ/kg × 1000 = 60,300 J/kg.

About Air Enthalpy

Is the enthalpy of moist and dry air the same? No. The specific enthalpy of dry air and moist air will be different because moist air contains water vapor, so its enthalpy depends on both temperature and humidity.