Expressions are developed for the internal efficiencies of magnetoelastic Rayleigh-wave convolvers. A bulk-wave formalism is used to express the nonlinear magnetization components m responsible for the convolution, as the square of the input signals S1 and S2, i.e., m=η (S 1+S2)2. The resulting expressions for η have a resonance-type denominator of the form ω2- ω20, where ω0 is the gyrofrequency. Such a resonance does not occur with surface magnetoelastic waves. The results are adapted to the surface-wave case by means of an approximation to estimate the nonzero value of the denominator. Experimental values of η range from 1.2×105 to 4.7×105 Wb/m2 for the best convolvers reported to date. Corresponding theoretical values range from 9.5×104 to 1.58×105 Wb/m2. Uncertainties in the experimental and theoretical estimates are discussed.