The compressibility factor (Z), also known as the compression factor, is the ratio of the molar volume of a gas to the molar volume of an ideal gas at the same temperature and pressure. It is a useful thermodynamic property for modifying the ideal gas law to account for the real gas behavior.
The compressibility factor is defined as:
-
where 
is the molar volume, 
is the molar volume of the corresponding ideal gas, 
is the pressure, 
is the temperature, and 
is the gas constant.