Each Thomas Bird shoe style is based on a three dimensional 'last'. This determines the look and the fit. Some styles share the same last. These descriptions give some guidance to fit and sizing.
Slightly chiselled toe. Standard width and toe. Hampton penny loafers.
Slightly chiselled toe. Standard width and fit. A little more generous on width. Harrow oxford.
Slightly chiselled toe. Standard width and fit. Brooklyn monkstrap.
Rounded toe. Standard width and fit. Cambridge wingtip oxford.