A boundary effect model recently developed for scaling of quasi-brittle fracture is used to study the common size effect on strength and fracture toughness of finite-sized specimens. An equivalent crack length is adopted following the boundary effect model and used to measure the distance of a crack tip to the front and back specimen boundaries. This equivalent crack leads to a simplified asymptotic solution for finite-sized specimens akin to that for a large plate with a small edge crack. The two common failure criteria, the strength and the linear elastic fracture mechanics (LEFM) K-IC criteria, are taken as two asymptotic limits. The transition from the strength to toughness criterion is then given by the asymptotic solution. The recent asymptotic model for finite-sized specimens/structures is applied to geometrically similar specimens of a fixed alpha-ratio, and specimens of identical size, but different alpha-ratios. (c) 2005 Elsevier Ltd. All rights reserved.