Two feet that length assigns the same number can occupy a shoe in very different ways. In the RMIT University study, forefoot circumference varied by up to 40 millimetres among women grouped into the same US size and by up to 37 millimetres within the same European size.
The research involved 107 healthy women aged 18 to 54, recruited in the metropolitan area of Melbourne. The researchers measured foot and arch length, forefoot width and circumference using a modified fitting device and a tape measure; before measurement, each participant had indicated the size she normally bought. The study was published online on 28 July; RMIT released the findings on 31 August.
The comparison revealed frequent mismatches. Among the 68 participants with a comparable US size, 72 per cent reported a number different from the one assigned based on length. Among the 64 with a comparable European size, that was the case in 65 per cent of instances. The difference more often went upward: 59 per cent in the US system and 52 per cent in the European system chose a larger size.
Buying a longer shoe can compensate for insufficient width, the authors explain. The data do not allow the reason for each participant's choice to be established: personal preferences, toe box shapes, and differences between brands all play a role. It does, however, expose the limitation of a number that orders primarily length while the foot has width and volume. To cover the full variation observed within the same length, the researchers estimate that roughly six width options would be needed in the US system and seven in the European one.
The results describe a small sample, made up exclusively of healthy women from Melbourne and recruited for convenience; they do not represent all Australian feet. The comparison concerns measurements and self-reported sizes, while the actual fit of individual shoes remains outside the scope of the experiment. The compromise the study points to is a practical one: some people may end up with more room in front of their toes simply because it is the only available way to fit the forefoot in.