Gas Compressibility Factor (Z) Calculator

Calculation controls

Input mode

Use reduced mode if you already know Ppr and Tpr.

Pressure

Unit

Temperature

Unit

Methods

DAK

DPR

Hall–Yarborough

DAK and DPR are implicit correlations requiring iteration. citeturn13view2turn17search18

Display precision

Plot settings

If Pmax is blank, it auto-scales.

Gas description & pseudo-critical setup

Quick entry

Gas gravity mode

Gas gravity (γg)

Ppc/Tpc correlation

CO₂ (fraction)

H₂S (fraction)

N₂ (fraction)

Sour/impurity correction

Wichert–Aziz equations shown in standard production engineering texts. citeturn18view0turn11view0

Advanced entry

Enable composition

Uses Kay’s mixing rule for Ppc/Tpc; enables PR/SRK EOS (optional).

Component	yᵢ

Cubic EOS (optional)

Compute EOS Z

EOS cubic forms are shown alongside HY in production engineering references. citeturn18view0

Enable composition to enter mole fractions for CH₄, C₂H₆, CO₂, N₂, H₂S, etc.

Batch CSV (optional)

Paste rows as: P,T. If you choose Reduced mode, paste Ppr,Tpr instead. First line may be a header.

How to use this calculator

Choose Direct (P, T) or Reduced (Ppr, Tpr) input mode.
Enter gas description: Gas gravity + impurities, or enable composition for detailed inputs.
Select a correction: Wichert–Aziz for CO₂/H₂S, or CKB for CO₂/H₂S/N₂ approximations. citeturn18view0turn11view0
Pick one or more Z methods (DAK, DPR, HY) and press Calculate Z.
Use exports (CSV/PDF), batch mode, and the Z–P plot for quick checks.

Formulas used (summary)

Reduced properties: Ppr=P/Ppc, Tpr=T/Tpc.
Wichert–Aziz correction: Tpc' = Tpc − ε, Ppc' = Ppc·Tpc'/(Tpc + yH2S(1−yH2S)ε). citeturn18view0
Hall–Yarborough: solve reduced density y, then Z = 0.06125·Ppr·t·exp(-1.2(1−t)^2)/y. citeturn18view0
DAK: implicit EOS fit to Standing–Katz; solved by iteration. citeturn13view2
DPR: 8-constant BWR-type implicit form; solved by iteration. citeturn17search18turn13view1
SRK/PR EOS (optional): solve cubic in Z and select gas-phase root. citeturn18view0

Example data table

Typical check case: γg=0.70, T=75°F, P=2000 psia, CO₂=0.05, H₂S=0.00.

Case	P	T	γg	CO₂	H₂S	N₂
Example	2000 psia	75 °F	0.70	0.05	0.00	0.00

Run this example and compare DAK/DPR/HY values for a quick sanity check.