The methods for the theoretical prediction of delivered specific impulse are relatively well known. They involve computing the losses due to two-phase flow, divergence, boundary layer, kinetics, nozzle submergence, and combustion inefficiency. The largest computed loss in typical aluminized solid propellants is the two-phase flow loss; this computation also has the largest uncertainty because the particle size and distribution are not precisely known. In this paper, a correlation of mean particle diameter vs throat diameter from experimental data was used with the solid-rocket performance prediction program to predict the propellant specific impulse of a number of motors. These predictions are compared to the experimental values. The results indicate that the specific impulse efficiency appears to be an inherent property of the propellant. In addition, the experimental specific impulse and specific impulse efficiency were statistically correlated against motor and propellant variables. These correlations are as accurate as the longer, more expensive, theoretical analysis. In addition to specific impulse prediction, the correlation equations are useful in optimization of motor designs.