For the first time, detailed and consistent experimental data are presented on the effect of column size on the homogeneous-heterogeneous regime transition in bubble columns. Systematic measurements were performed in air-water bubble columns of diameters 0.14, 0.29 and 0.4 m and heights between 0.1 and 1.2 m. The critical point where the homogeneous regime looses stability and the transition begins was evaluated from the drift-flux plot. The results show that both the column height and width destabilize the homogeneous regime and advance the transition. Our data were compared with predictions of two available stability theories. Both the theories agree with the data relatively well. Our results also suggest that the column aspect ratio alone cannot replace the simultaneous effect of the column height and width,