This paper presents the results of an investigation into the scale-up of bread dough mixers. Previous research reports into dough mixer scale-up only consider the dough development aspect of mixing and neglect aeration, despite over-aeration being a known problem that occurs with scale-up. A series of experiments was performed on three scales of the Tweedy-type high-intensity mixer. A pressure step-change was introduced during mixing, and dimensionless aeration parameters for each mixer were found through measurement of the dough voidage response, using a previously reported aeration model. The degree of steady state aeration, the turnover rate and the volumetric entrainment rate were all found to increase with mixer scale, or alternatively with Reynolds number. The number density of bubbles in the dough and the mean bubble size could not be seen to vary significantly with scale, but both increased with mixer headspace pressure.