What is the compressibility factor (Z)?

Z = PV/RT. It measures how much a real gas deviates from ideal gas behavior. Z = 1 for ideal gases, Z 1 at moderate pressure and high temperature.

Which method is best for natural gas?

Dranchuk-Abu-Kassem is the most accurate for natural gas and hydrocarbon mixtures in the range 0.2 ≤ Pr ≤ 30 and 1.05 ≤ Tr ≤ 3.0.

When should I not use the ideal gas law?

When Z deviates more than 5% from 1.0 (common at pressures > 50 bar or near critical point). Always use Z-factor for pipeline, reservoir and compressor calculations.

Gas Compressibility Factor Calculator

Calculate gas deviation from ideal behavior with precision. Fast, accurate, and reliable calculations for professionals and students.

Compressibility Factor: 45.67 × 12.3

0.956

3 Calculation Methods

Featured: Dranchuk-Abu-Kassem, Benedict-Webb-Rubin, Peng-Robinson

Temperature (°C)

Pressure (bar)

Molecular Weight (g/mol)

Critical Temperature (K)

Critical Pressure (bar)

Acentric Factor

Z-Factor vs. Temperature

Dranchuk-Abu-Kassem Method

Empirical correlation based on the Standing-Katz chart. Accurate for natural gas systems.

Z = 1 + (A1 + A2/Tr + A3/Tr³)ρr + (A4 + A5/Tr)ρr² + A5A6ρr⁵/Tr + A7ρr²/Tr³(1 + A8ρr²)exp(-A8ρr²)

Benedict-Webb-Rubin EOS

8-parameter equation of state suitable for both gas and liquid phases.

P = RTρ + (B0RT - A0 - C0/T²)ρ² + (bRT - a)ρ³ + aαρ⁶ + (cρ³/T²)(1 + γρ²)exp(-γρ²)

Peng-Robinson Equation

Cubic equation of state widely used in petroleum and chemical industries.

P = RT/(V - b) - aα/[V(V + b) + b(V - b)]
where α = [1 + κ(1 - √Tr)]², κ = 0.37464 + 1.54226ω - 0.26992ω²

Enter parameters and click "Calculate Z-Factor" to see results

Compressibility Factor Calculation Methods

Dranchuk-Abu-Kassem

Empirical correlation based on the Standing-Katz chart. Accurate for natural gas systems.

Benedict-Webb-Rubin

8-parameter equation of state suitable for both gas and liquid phases.

Peng-Robinson

Cubic equation of state widely used in petroleum and chemical industries.

Dranchuk-Abu-Kassem Method

Z = 1 + (A1 + A2/Tr + A3/Tr³)ρr + (A4 + A5/Tr)ρr² + A5A6ρr⁵/Tr + A7ρr²/Tr³(1 + A8ρr²)exp(-A8ρr²) Empirical correlation based on the Standing-Katz chart. Accurate for 1.05 ≤ Tr ≤ 3.0 and 0.2 ≤ Pr ≤ 30.

Benedict-Webb-Rubin EOS

P = RTρ + (B0RT - A0 - C0/T²)ρ² + (bRT - a)ρ³ + aαρ⁶ + (cρ³/T²)(1 + γρ²)exp(-γρ²) 8-parameter equation suitable for both gas and liquid phases. Constants are estimated from critical properties.

Peng-Robinson EOS

P = RT/(V - b) - aα/[V(V + b) + b(V - b)] where a = 0.45724 R²Tc²/Pc, b = 0.07780 RTc/Pc, α = [1 + κ(1 - √Tr)]², κ = 0.37464 + 1.54226ω - 0.26992ω²