Gas Volume Calculator

Calculate gas volume at standard conditions using the real gas equation (PV = ZnRT)

Gas Conditions

Enter actual or standard conditions to convert

Input Conditions
Gas Properties
Air = 1.0, Natural gas ~0.6-0.8
Ideal gas Z = 1.0

Volume Results

Enter conditions and click Calculate

Compressibility Factor (Z)

The Z factor accounts for deviation from ideal gas behavior. At low pressures and moderate temperatures, Z is close to 1.0. At high pressures, Z can deviate significantly.

  • Ideal gas: Z = 1.0
  • Typical reservoir gas: Z = 0.7 - 0.9
  • Calculate Z using Standing-Katz charts or correlations

Formula Reference

Real Gas Equation of State

PV = ZnRT Where: P = Pressure (absolute) V = Volume Z = Compressibility factor n = Number of moles R = Universal gas constant (10.73 psia-ft3/lbmol-R) T = Temperature (absolute - Rankine)

Volume Conversion (Actual to Standard)

V_sc = V_ac x (P_ac / P_sc) x (T_sc / T_ac) x (Z_sc / Z_ac) Since Z_sc = 1.0 at standard conditions: V_sc = V_ac x (P_ac / P_sc) x (T_sc / T_ac) / Z_ac Where: V_sc = Volume at standard conditions V_ac = Volume at actual conditions P, T = Pressure, Temperature at each condition Z_ac = Compressibility at actual conditions

Gas Formation Volume Factor (Bg)

Bg = (P_sc x Z x T) / (P x T_sc) Bg = 0.02827 x (Z x T) / P [for API standard conditions] Where Bg = res bbl / SCF or ft3/SCF

Gas Density

rho = (P x M) / (Z x R x T) Or: rho = 2.70 x (P x SG) / (Z x T) [lb/ft3] Where: M = Molecular weight = 28.97 x SG (for gas) SG = Gas specific gravity (air = 1.0)

Standard Conditions Reference

Standard Pressure Temperature
API (US Oil/Gas)14.696 psia60F (520R)
STP (Scientific)14.696 psia32F (492R)
NTP (Normal)14.696 psia68F (528R)
ISO (Metric)101.325 kPa15C (288K)