Measurements and Sizing

The sizes of the left and right feet are often slightly different. In this case, both feet are measured, and purchasers of mass-produced shoes are advised to purchase a shoe size based upon the larger foot because, contrary to the reality of foot sizes, most manufacturers do not sell pairs of shoes in non-matching sizes. Each size of shoe is considered suitable for a small interval of foot lengths. The inner cavity of a shoe must typically be 15–20 mm longer than the foot, but this relation varies between different types of shoes

THERE ARE THREE CHARACTERISTIC LENGTHS A SHOE SIZE CAN REFER TO:

1. The median length of feet for which a shoe is suitable. For customers, this measure has the advantage of being directly related to their body measures. It applies equally to any type, form, or material of the shoe. However, this measure is less popular with manufacturers, because it requires them to test carefully for each new shoe model, for which range of foot sizes it is recommendable. It puts on the manufacturer the burden of ensuring that the shoe will fit a foot of a given length.
2. The length of the inner cavity of the shoe. This measure has the advantage that it can be measured easily on the finished product. However, it will vary with manufacturing tolerances and provides the customer only very crude information about the range of foot sizes for which the shoe is suitable.
3. The length of the "last", the foot-shaped template over which the shoe is manufactured. This measure is the easiest one for the manufacturer to use because it identifies only the tool used to produce the shoe. It makes no promise about manufacturing tolerances or for what size of the foot the shoe is actually suitable. It leaves all responsibility and risk of choosing the correct size with the customer. Further, the last can be measured in several different ways resulting in different measurements.

All these measures differ substantially from one another for the same shoe.

LENGTH

Sizing systems also differ in what units of measurement they use. This also results in different increments between shoe sizes because usually, only "full" or "half" sizes are made.

The following length units are commonly used today to define shoe-size systems:

• The Paris point equates to 2⁄3 centimetre (6.6 mm or ~0.26 in). This means an increment of 2⁄3 centimetre (1⁄4 inch) in whole sizes and 1⁄3 centimetre (1⁄8 inch) between half sizes. This unit is commonly used in Continental Europe.
• The Barleycorn is an old English unit that equates to 1⁄3 inch (8.46 mm). Half sizes are commonly made, resulting in an increment of 1⁄6 inch (4.23 mm). This measure is the basis for current U.K. and U.S. shoe sizes, with the largest shoe size taken as twelve inches (a size 12) and then counting backwards in barleycorn units.
• Further, metric measurements in centimetres (cm) or millimetres (mm) are used. The increment is usually 0.5 cm (5 mm or ~0.20 in), which is between the step size of the Parisian and the English system. It is used with the international Mondopoint system and with the Asian system.

Due to the different units of measurements, converting between different sizing systems results in rounding errors as well as unusual sizes such as "10 2⁄3".

ZERO POINT

The sizing systems also place size 0 (or 1) at different locations:

If size 0 is placed at a foot's length of 0, the shoe size is directly proportional to the length of the foot in the chosen unit of measurement. Sizes of children's, men's, and women's shoes, as well as sizes of different types of shoes, can be compared directly. This is used with the Mondopoint and the Asian system. However, size 0 can also represent a length of the shoe's inner cavity of 0. The shoe size is then directly proportional to the inner length of the shoe. This is used with systems that also take the measurement from the shoe. While sizes of children's, men's and women's shoes can be compared directly, this is not necessarily true for different types of shoes that require a different amount of "wiggle room". This is used with the Continental European system.

Further, size 0 (or 1) can just be a shoe with a given length, typically the shortest length deemed practical. This can be different for children's, teenagers', men's, and women's shoes, making it impossible to compare sizes. For example, a women's shoe at size 8 is a different length from a men's shoe at size 8 in the US system, but not the British.

WIDTH 

Some systems also include the width of a foot. There are different methods indicating the width:

The measured width is indicated in millimetres (mm). This is done with the Mondopoint system.

The measured width is assigned a letter (or combination of letters), which is taken from a table (indexed to length and width) or just assigned on an ad-hoc basis: Examples include (each starting with the narrowest width): 
A, B, C, D, E, EE, EEE, EEEE, F, G (typical North American system; medium being D)
4A, 3A, 2A, A, B, C, D, E, 2E, 3E, 4E, 5E, 6E (variant North American)
C, D, E, F, G, H (common Aus/UK "medium" is usually E or F, but varies by manufacturer one maker's E is not necessarily the same size as another's.
N (narrow), M (medium) or R (regular), W (wide)

The width for which these sizes are suitable can vary significantly between manufacturers. The A-E width indicators used by most American, Canadian, Australian and some British shoe manufacturers are typically based on the width of the foot, and common step sizes are 3⁄16 inch.

This is the second article in our ongoing series: "The Complete Shoemaking Process". The next entry in the series is about taking measurements for last making.