Flow Measurement · Glossary

What is Compressibility Factor?

Symbol: ZdimensionlessFlow Measurement

Compressibility factor Z corrects the ideal gas law for real gas behaviour; Z = 1 for an ideal gas.

Compressibility Factor Explained

At low pressure most gases behave close to ideal. At higher pressures or low temperatures molecules interact, and the real density differs from the ideal gas value.

Z is taken from equations of state, such as AGA 8 or ISO 12213 for natural gas. It is used in density, standard volume and DP compensation calculations.

Compressibility Factor Formula

p V = Z n R T and ρ = p M ÷ (Z R T)

p	absolute pressure
M	molar mass
R	8.314 J/(mol·K)
T	absolute temperature

Calculators for Compressibility Factor

CalculatorGas Density CalculatorFree online calculator with formula and worked example.CalculatorGas Flow Conversion CalculatorFree online calculator with formula and worked example.

Frequently Asked Questions

What is Compressibility Factor?

Compressibility factor Z corrects the ideal gas law for real gas behaviour; Z = 1 for an ideal gas.

When can Z be taken as 1?

For air and many gases near atmospheric pressure the error is small. At pipeline pressures Z must be calculated.

Can Z be above 1?

Yes, at high pressures for many gases, and for hydrogen even at moderate pressure.

Learn more on the blog

Types of flow meters

A practical guide on instrumentationblog.in with more detail on compressibility factor and how it is applied on real plants.

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