Shoe size

A shoe size is an indication of the fitting size of a shoe for a person.
There are a number of different shoe-size systems used worldwide. While all shoe sizes use a number to indicate the length of the shoe, they differ in exactly what they measure, what unit of measurement they use, and where the size 0 is positioned. Some systems also indicate the shoe width, sometimes also as a number, but in many cases by one or more letters. Some regions use different shoe-size systems for different types of shoes. This article sets out several complexities in the definition of shoe sizes. In practice, shoes are often tried on for both size and fit before they are purchased.

Deriving the shoe size

Foot versus shoe and last

The length of a person's foot is commonly defined as the distance between two parallel lines that are perpendicular to the foot and in contact with the most prominent toe and the most prominent part of the heel. Foot length is measured with the subject standing barefoot and the weight of the body equally distributed between both feet.
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 on the larger foot, as most retailers do not sell pairs of shoes in non-matching sizes.
Each size of shoe is considered suitable for a small interval of foot lengths, typically limited by half-point of the shoe size system.
A shoe-size system can refer to three characteristic lengths:

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 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.
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 only gives the customer very crude information about the range of foot sizes for which the shoe is suitable.
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 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. For example, the inner cavity of a shoe must typically be 15 mm longer than the foot, and the shoe last would be 2 size points larger than the foot, but this varies between different types of shoes and the shoe size system used. The typical range lies between for the UK/US size system and for the European size system, but may extend to and.

Length

Sizing systems also differ in the 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. Whole sizes are incremented by 1 Paris point; this corresponds to between half sizes. This unit is commonly used in Continental Europe, and Russia and former USSR countries.
The barleycorn is an old English unit that equates to. This is the basis for current UK and North American shoe sizes. "Today in America, the sizing generally adheres relatively closely to a formula of 3 times the length of the foot in inches, less a constant. In the UK, shoe sizes follow a similar method of computation, except that the constant is 23, and it is the same for men and women".
Metric measurements in millimetres or centimetres, with intervals of 5 mm and 7.5 mm are used in the international Mondopoint system.

Since the early 2000s, labels on sports shoes typically include sizes measured in all four systems: EU, UK, US, and Mondopoint.

Zero point

The sizing systems also place size 0 at different locations:

Size 0 as 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 system.
Size 0 as the 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" in the toe box. This is used with the Continental European system.
Size 0 can just be simply a shoe of a given length. Typically, this will be the shortest length deemed practical; but this can be different for children's, teenagers', men's, and women's shoes - making it difficult to compare sizes. In America, the baseline for women's shoes is seven inches and for men's it is 7 in.; in the UK, the baseline for both is 7 in.
Width

Some systems also include the width of a foot, but they do so in a variety of ways:

Measured foot width in millimetres – this is done with the Mondopoint system.
Measured width expressed as a letter, which is taken from a table or just assigned on an ad-hoc basis. Examples are :
* AAA, AA, A, B, C, D, E, EE, EEE is the typical North American system and follows the Brannock device standards; on this system, B is narrow, C is regular, D is medium, E is wide, EE is extra wide and so on. The unlettered D size is the norm for men, and B for women.
* 4A, 3A, 2A, A, B, C, D, E, 2E, 3E, 4E, 5E, 6E.
* C, D, E, F, G, H.
* N, M or R, W, XW.
* For children's sizes in North America, typical letters used are M or B, W or D, EW or 2E.

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

N-M-R-W system	North American system	North American variant	UK system	German system
SS	AAAA	4A
S	AAA	3A
N	AA	2A	B	E
N	A	A	C	E
M	B	B	D	F
M	C	C	D	F
R	D	D	D	F
W	E	E	E	G
XW/EW / WW	EE	2E	EE	H
UW / WWW	EEE	3E	EEE	J
UW / WWW	EEEE	4E		K
XXW	EEEEE	5E		L
XXW	EEEEEE	6E		M

Difficulties

There could be differences between various shoe size tables from shoemakers and shoe stores. They are usually due to the following factors:

Different methods of measuring the shoes, different manufacturing processes, or different allowances even when the same system is used.
An indication in centimetres or inches can mean the length of the foot or the length of the shoe's inner cavity.
Differing amounts of wiggle room required for different sizes of shoes.
For wide feet, a shoe several sizes larger may be required and may also result in inconsistent size indications when different typical widths are attributed to specific shoe sizing systems.
Some tables for children take future growth into account. The shoe size is then larger than what would correspond to the actual length of the foot.

Conversion tables available on the Web often contain obvious errors, not taking into account different zero points or wiggle room.
Although shoe size systems are not fully standardised, the ISO/TC 137 had released a [|technical specification ISO/TS 19407:2015] for converting shoe sizes across various local sizing systems. Even though the problem of converting shoe sizes accurately has yet to be fully resolved, this standard serves as "a good compromise solution" for shoe-buyers.

Common sizing systems

United Kingdom

Shoe size in the United Kingdom, Ireland, India, Pakistan and South Africa is based on the length of the last used to make the shoes, measured in barleycorns starting from the smallest size deemed practical, which is called size zero. It is not formally standardised. The last is typically longer than the foot's heel-to-toe length by to in or to 2 barleycorns, so to determine the shoe size based on actual foot length one must add 2 barleycorns.
A child's size zero corresponds to a last length of, and the sizes go up to size . Thus, the calculation for a children's shoe size in the UK is:
equivalent to:
An adult size 1 is then the next half-size up and each size up continues the progression in barleycorns. The calculation for an adult shoe size in UK sizing is thus:
equivalent to:
Although this sizing standard is nominally for both men and women, some manufacturers use different numbering for women's UK sizing.
In Australia and New Zealand, the UK system is followed for men and children's footwear. Women's footwear follows the US sizings.