The shear bond strength of FRP-to-concrete bonded joints is generally obtained through single shear tests, for which the specimen can be viewed as a layered structure. Based on the fracture mechanics theory for laminated structures, two simple formulae to estimate shear bond strength are suggested respectively for two main failure modes encountered in the testing. The formulae exclude all empirical parameters except the one accounting for the width effect, therefore bearing a more rational and physically strict sense. Finite element analysis is performed to determine the fracture toughness which is the most important parameter in the formulae. The cohesive zone model (CZM) is employed in the simulation. A comparison with experimental observations and results predicted by existing formulations is made and good agreement is achieved.