Disclaimer: Not to be confused with Compressibility factor .

A measure of resistance of a Continuum body to compression/decompression.

A measure of relative change in density or molar volume under a unit pressure variation:

c = \frac{1}{\rho} \left( \frac{\partial \rho}{\partial p} \right) = - \frac{1}{V_m} \left( \frac{\partial V_m}{\partial p} \right)

Symbol	Dimension	SI units	Oil metric units	Oil field units
	M^-1 L¹T²	Pa^-1	kPa^-1	psi^-1

Compressibility depends on the thermodynamic conditions at which it is measured and as such is not a material property.

The two major medium compression/decompression processes are isothermal and isentropic which result in different values of compressibility:

c_T = \frac{1}{\rho} \left( \frac{\partial \rho}{\partial p} \right)_T

c_S = \frac{1}{\rho} \left( \frac{\partial \rho}{\partial p} \right)_S

Both and are not dependent on the amount of chemical substance and defined under a clear conditions of thermodynamic process and as such are the material properties and properly tabulated for the vast majority of materials.

In most practical cases the Compressibility normally means Isothermal Compressibility: .

c(p) = \frac{1}{p} - \frac{1}{Z} \frac{dZ}{dp}

c(p) =  - \frac{1}{B} \frac{dB}{dp}

See also