A new approach based on the thermodynamic theory of vacancy solutions and Hooke's law is developed for the description of the elastic strain of isotropic solid adsorbents during physical adsorption. The equation linking a relative strain with the equilibrium parameters of adsorption is derived. The explicit expression allowing calculation of the contribution from solid strain to heat of adsorption is obtained. Validity of the developed method has been confirmed by comparing the theoretically predicted dimensional changes on adsorption to the experimentally studied system zeolite CaA–krypton where both contraction and expansion occurred.