For small deformations, most elastic materials exhibit linear elasticity and can be described by a linear relation between the stress and strain. These relationships are quantified with elastic constants like the elasticity tensor and its inverse quantity, the compliance tensor, as part of the theory of linear elasticity. These tensors can be used to calculate numbers such as the bulk modulus, shear modulus, Young's modulus, and Poisson's ratio, which are especially useful to describe the elastic behavior of isotropic materials.