The proper assessment of shear coupling is necessary for the evaluation of laminated glass performance between the bounding layered and monolithic limits. The most common simplified design approach consists in defining the effective thickness, i.e., the thickness of a monolithic section with equivalent flexural properties. Cantilevered laminated glass balustrades are common applications of structural glass. However, the use of existing effective thickness methods presents strong limitations for their design. Here, the conjugate beam effective thickness (CBET) method is presented, based on the conjugate beam analogy recently proposed to evaluate the response of inflected laminates formed by external elastic beams bonded by an adhesive ply. The conjugate beam analogy, applied to laminated glass beams, allows accurate evaluation of the shear stress transmitted by the interlayer, based on the response of a monolithic conjugate beam, with the option to constrain relative sliding of plies at a beam end. Once the shear coupling is known, the effective thickness may be evaluated with the proposed CBET model by comparing the maximum stress and deflection of the laminated beam with a monolithic Euler–Bernoulli beam. The CBET method’s formulas can be readily applied to evaluate the maximum stress and cantilever free-end deflection for different load and boundary conditions, representative of cantilevered laminated glass balustrade supported in a U-profile.