Based on the experimental observation that the just-suspension speed is not affected by the baffle insertion depth, we proposed a new correlation method to estimate the Zwietering's geometrical constant S for solid suspensions in solid-liquid stirred vessels. The proposed equation is a function of power number under fully baffled condition N-P,N-fbc, c(b)/D and d/D (c(b), impeller off-bottom clearance; D, vessel diameter; d, impeller diameter). The geometrical constant for solid suspension estimated in this work agrees with the measured data reported in the literature. The just-suspension speed in solid-liquid stirred vessels with various types of impellers can be estimated by the proposed equation.