(see Compressibility @ Wikipedia)
A measure of fluid density \rho_f change due to pressure p variation:
| (1) | c_f = \frac{1}{\rho_f} \frac{\partial \rho_f}{\partial p} |
This can be redefined in terms of fluid volume
V_f:
| (2) | c_f = -\frac{1}{V_f} \frac{\partial V_f}{\partial p} |