Size effect on the specific fracture energy G(F) of Concrete can be adequately modelled by an uneven fracture energy distribution along the crack path induced by the specimen boundary influence. The boundary influence on G(F) can be neglected only if a specimen is very large so that the boundary region is a very small portion of the total fracture area. The underlying principle on the specimen boundary induced size effect provides a simple and logical explanation for the commonly observed size effect on G(F). The boundary effect model recently proposed by the authors is used in this paper to quantitatively evaluate the specimen boundary influence so that the size-independent fracture energy is derived, which otherwise can only be measured with very large concrete specimens. New experimental results from a very different material system, polymer, are analysed together with concrete results by the simple boundary effect model. (c) 2006 Elsevier Ltd. All rights reserved.