Although only 2 independent elastic constants are required to completely the properties of an isotropic, elastic medium, there are many different constants from which to choose. Most of these constants arise as constants of proportionality between stress and strain for various loading conditions. For example, the ratio of hydrostatic stress (pressure) to volumetric strain (dilatation) is , which is given the name bulk modulus and the symbol . The constants referred to below are:
To these we may add the following combinations that appear frequently.