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Ideal Gas Law Calculator

PV = ZnRT | GPSA

Ideal & Real Gas Law Calculator
Calculate gas properties using PV=nRT (ideal) or PV=ZnRT (real gas with compressibility factor). Includes standard/actual volume conversions and gas density calculations per GPSA.

Calculation Mode

Known Values

psia
ft³
lbmol
°F

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Formulas

PV = ZnRT
P = Absolute pressure (psia)
V = Volume (ft³)
Z = Compressibility factor (1.0 for ideal gas)
n = Number of moles (lbmol)
R = 10.73159 psia·ft³/(lbmol·°R)
T = Absolute temperature (°R = °F + 459.67)
ρ = PM / (ZRT)
ρ = Gas density (lb/ft³)
M = Molecular weight (lb/lbmol)

Standards & References

  • GPSA
    14th Edition, Section 23 - Physical Properties
  • AGA Report No. 8
    Compressibility Factors of Natural Gas (Z-factor)
  • API MPMS Chapter 14.3
    Orifice Metering of Natural Gas
  • ISO 12213
    Natural Gas - Calculation of Compression Factor

Important Notes

  • Ideal gas: Accurate within 1-2% for P < 100 psia, T > 100°F
  • Real gas: Use Z-factor for P > 100 psia (5-15% error if ignored)
  • Temperature: Must be absolute (°R = °F + 459.67)
  • Pressure: Must be absolute (psia = psig + 14.7)
  • Standard conditions: 14.73 psia, 60°F per GPSA petroleum
  • Molar volume: 379.5 ft³/lbmol at standard conditions
  • Z-factor estimation: Uses Dranchuk-Abou-Kassem correlation

Quick Reference

Gas MW SG
Methane (CH₄) 16.04 0.554
Ethane (C₂H₆) 30.07 1.038
Propane (C₃H₈) 44.10 1.522
Natural Gas (typ) 17-20 0.60-0.70
Air 28.97 1.000
Nitrogen (N₂) 28.01 0.967

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