C295 – GPA TP-25 – NGL and LPG Density Referral


This calculates the density of an NGL or LPG at standard conditions or at process temperature and pressure using the guidelines set out in the below GPA and API standards.


GPA – TP-25/API MPMS Chapter 11.2.4 – Temperature Correction for the Volume Of Light Hydrocarbons – Tables 24E and 23E (1998)

Measurement of Petroleum Measurement Standards Chapter 11.2.1 – Compressibility Factors for Hydrocarbons: 0-90° API Gravity Range (1984)

API MPMS Chapter 11.2.1M – Compressibility Factors for Hydrocarbons: 638 – 1074 Kilograms per Cubic Metre Range (1984)

Measurement of Petroleum Measurement Standards Chapter 11.2.2 – Compressibility Factors for Hydrocarbons: 0.350-0.637 Relative Density (60°F/60°F) and -50°F to 140°F Metering Temperature (First Edition October 1986)

API MPMS Chapter 11.2.2M – Compressibility Factors for Hydrocarbons: 350 – 637 Kilograms per Cubic Metre Density (15°C) and -46°C to 60°C Metering Temperature (1986)

Kelton calculation reference C295

FLOCALC calculation reference F091


Solve for

  • Density
  • Standard density

This option is used to select whether the calculation will solve for density at process or standard conditions.


  • Full precision
  • Full rounding
  • Rounding of inputs

This option is used to decide upon the rounding procedure to be employed. The full precision calculation doesn’t round any values. Full rounding rounds the inputs and outputs as described in the relevant standards. Rounding of inputs only rounds the input temperature and density according to the procedure set out in GPA TP-25. Note that the range of the density inputs at standard conditions vary from one standard temperature to another. Consult the relevant standards for details of the range of the input parameters of the calculation as the ranges associated with standards used in this procedure do not overlap at all temperatures and densities. Note that when rounding is used for certain input values the calculation does not converge, this issue is overcome by selecting full precision. An intermediate will be displayed to show whether the calculation has converged sufficiently.

Vapour Pressure

  • Include

Select this option to include vapour pressure input. If this is not selected the calculation will use a default value of 1 atmosphere (1.01325 bar).

API Compressibility

  • Metric
  • US Customary

This option is used to select whether the pressure correction is to use the metric versions of API compressibility standards, MPMS Chapters 11.2.1M or 11.2.2M, or the standards in US customary units 11.2.1 and 11.2.2.


The calculation is carried out as described in C294.