According to Rossi (2000, p.202) standard width fittings were introduced in 1880. The ball width on the last determines ball width on the shoe. This measurement is not a linear side to side measurement across the foot but instead the girth which captures the volume of the forefoot. Several standard and width fittings are available in the UK size system to accommodate differences in three-dimensional girth. In women's shoes, A is the narrowest and G the widest. For children the range is A to H; and for men it is from 1-8. The girth increase between fittings is normally 6.5mm (one fourth of an inch). Most lines are only available in one size usually women's D and men's 4. The girth around the ball of the foot of the foot increases by 5mm for whole sizes up to children's size 101/2 and 6.5mm for whole sizes above this. In the American system it is two less, eg AAA is the equivalent to the UK A. There is no equivalent Continental width fitting system and the shoes are generally narrower than in the UK. In the American (or Standard) System the first number in the code represents the width (1 = A, 2 = B) The second number followed by a zero denotes the whole size: when the second number is followed by a 5 it indicates a half size. In the American (Arithmetic standard width measurement) this ranges from AAAAA to EEEEEE.
Rossi W A (ed) 2000 The complete footwear dictionary (2nd ed) Kreiger Publishing Co. Florida.