C306 – GPA 2172 – Compressibility (with AGA8 option), Gross Heating Value and SG of Natural Gas from Composition


This calculates heating value, compressibility, relative density and theoretical liquid content from a gas composition. Results are calculated for the composition treated as both a real and an ideal gas.  If required, the compressibility can be calculated using the AGA8 method and the compressibility of air can be user entered rather than using the GPA 2172 method.


FLOCALC Calculation reference F109

Kelton calculation reference C307

GPA 2172 – Gross Heating Value, SG and Compressibility of Natural Gas from Composition

GPA 2145 – Table of Physical Properties for Hydrocarbons and Other Compounds of Interest to the Natural Gas and Natural Gas Liquids Industries. (’89, ’00, ’03, ’09, ’16)

AGA8 – Compressibility Factors of Natural Gas and Other Related Hydrocarbon Gases (1994)


Hydrocarbon Tail

  • No Tail
  • C6 Tail
  • C7 Tail
  • C9 Tail

Select the appropriate hydrocarbon tail. Where a tail is selected the percentage split of each component is entered, this is generally obtained from laboratory analysis.

Base Pressure

  • 14.65 psi
  • 14.696 psi
  • 14.73 psi
  • 15.025 psi

This option is used to select the reference pressure used for the calculation.

Extended Composition

This tickbox can be checked to include a wider range of compounds in the composition.

Data Source

  • GPA 2145-89
  • GPA 2145-00
  • GPA 2145-03
  • GPA 2145-09
  • GPA 2145-16

This option is used to select the version of GPA 2145 used which contains the tables of data required by the calculations.

Compositional Analysis

  • Dry
  • Saturated
  • Partially Saturated

This option is used to select whether there is water vapour present in the gas, and if so to what extent.  If ‘Saturated’ or ‘Partially Saturated’ are selected the water content will be calculated based on equations laid out in the standard


  • GPA 2172 (Default)
  • AGA 8: 1994

Select whether compressibility is calculated as per the GPA 2172 method or calculated using the AGA 8 method.

Compressibility of air

  • User Entered
  • GPA 2172

Select whether the compressibility of air is calculated using the GPA 2172 method or an input is made available to the user to enter a value of their choice.


This performs the calculations as per GPA 2172 standard.