The size of the bubbles generated in gas-liquid stirred vessels is mainly a function of the agitation level but the prediction of the equilibrium bubble size is not possible from theory. A few correlations have been suggested based on the concept of a critical Weber number, the validity of which have not been confirmed. We report experiments where bubbles of known initial sizes were introduced in non-coalescing conditions, and the subsequent changes in their size were monitored as a function of the agitation level or power input. The Sauter mean bubble diameters are predicted well by an equation developed using Kolmogoroff's theory of local isotropic turbulence, provided the energy dissipation rate per unit mass is calculated on the basis of impeller swept volume