A measure of resistance of a Continuum body to compression.

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

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

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.

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

See also