AGA Report No. 3 · AGA-7 · API MPMS 14.3
Understand gas volume correction, supercompressibility, and AGA measurement standards
The Fixed Pressure Factor corrects gas volumes measured at flowing conditions to standard base conditions per AGA Report No. 3 and AGA-7. It combines pressure, temperature, and supercompressibility corrections into a single multiplier: FPF = Fpv × Ftf × Fgr.
The most common US base conditions are 14.73 psia at 60°F per AGA and GPSA conventions. An alternate standard of 14.696 psia at 60°F is also used. Canada typically uses 14.696 psia at 15°C (59°F).
The supercompressibility factor (Fgr or Fpv²) corrects for real gas behavior by accounting for the ratio of compressibility factors at base and flowing conditions (Zb/Zf). At higher pressures, this correction becomes increasingly significant for accurate volume measurement.
Elevation affects the atmospheric pressure used to convert gauge pressure readings to absolute pressure. At higher elevations, lower atmospheric pressure means a given gauge reading represents less absolute pressure, which directly impacts the pressure correction factor.