Editing Shoe size (section)

==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 (geometry)|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,{{Citation needed|date=December 2007}} 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.<ref name="orthopedic">{{cite web|author=Andersson, Bendt|title=Recommendations to suppliers and manufacturers of orthopedic footwear concerning sizes of shoes and lasts|url=http://www.hi.se/Global/pdf/2004/04319-pdf.pdf|access-date=2009-01-06|language=sv|url-status=dead|archive-date=2012-06-16|archive-url=https://web.archive.org/web/20120616211214/http://www.hi.se/Global/pdf/2004/04319-pdf.pdf}}</ref> 

[[File:Shoe size.jpg|thumb|upright=0.4|Cavity space in a shoe]]
All these measures differ substantially from one another for the same shoe. For example, the inner cavity of a shoe must typically be 15&nbsp;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 {{convert|1/2|to|2/3|in|mm|1}} for the UK/US size system and {{cvt|4/3|to|5/3|cm|mm|1}} for the European size system, but may extend to {{convert|1/4|to|3/4|in|mm}} and {{cvt|2/3|to|6/3|cm|mm|1}}.

===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:{{cn|date=November 2023}}

* The [[Paris point]] equates to {{convert|2/3|cm|mm in|2}}. Whole sizes are incremented by 1 Paris point; this corresponds to {{convert|3.33|mm|in}} between half sizes. This unit is commonly used in Continental Europe, and Russia and former USSR countries.
* The [[Barleycorn (unit)|barleycorn]] is an old [[English unit]] that equates to {{convert|1/3|in|mm|2}}. 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 (the barleycorn length), less a constant (22 for men and 21 for women). 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".<ref name="Melissa">{{cite web |title=Why are shoe sizes as they are?  |last=Melissa |url=https://www.todayifoundout.com/index.php/2016/03/pedestrian-origins-modern-shoe-sizes/ |website=Today I found out |date=30 March 2016}} (12×3=36. US(m): 36−22=14, UK: 36−23=13, EU:30.5×1.5=45.75 then +2 "for comfort" plus rounding = 48)</ref>

* [[Metric system|Metric]] measurements in millimetres (mm) or centimetres (cm), with intervals of 5&nbsp;mm and 7.5&nbsp;mm are used in the international Mondopoint system (USSR/Russia and East Asia).

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 (or 1) 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 (USSR/Russia and East Asia).
* 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 (or 1) 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{{sfrac|3}} in.; in the UK, the baseline for both is 7{{sfrac|2|3}} in.<ref name="Melissa" />

===Width===
Some systems also include the width of a foot (or the girth of a shoe last), but do so in a variety of ways:
* Measured foot width in millimetres (mm) – this is done with the [[#Mondopoint|Mondopoint]] system.
* Measured width as a letter (or combination of letters), which is taken from a table (indexed to length and width/girth) or just assigned on an ad-hoc basis. Examples are (each starting with the narrowest width):
** AAA, AA, A, B, C, D, E, EE, EEE is the typical North American system and follows the [[brannock device]] standards, per the 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 (variant North American).
** C, D, E, F, G, H (common UK; "medium" is usually F but varies by manufacturer—makers [[Edward Green Shoes|Edward Green]] and Crockett & Jones, among others, use E instead, but one maker's E is not necessarily the same size as another's).
** N (''narrow''), M (''medium'') or R (''regular''), W (''wide''), XW (extra wide).
** For children's sizes in North America, typical letters used are M or B (medium), W or D (wide), EW or 2E (extra wide).

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 {{frac|3|16}} inch (4.8&nbsp;mm).
{| class="wikitable"
|+Foot width conversion – approximation<ref>{{Cite web |title=Schuhweiten richtig messen & Größentabelle – F, G und H |url=https://www.blitzrechner.de/schuhbreite/ |access-date=2024-03-27 |website=www.blitzrechner.de |language=de}}</ref><ref>{{Cite web |title=Men's UK Shoe Width |url=https://sizechart.com/shoes/shoe-width/men/uk/index.html |access-date=2024-03-27 |website=sizechart.com}}</ref><ref>{{Cite web |last=Franke |first=Rieke |date=2021-05-15 |title=Alles über Schuhweiten • Die Breite-Füße-Infothek |url=https://breitefuesse.de/schuhweite-messen/ |access-date=2024-03-27 |website=Breite Fuesse |language=de-DE}}</ref><ref>{{Cite web |last=Janine |date=2023-04-26 |title=Women's shoe widths explained + width letters chart for US, UK & Europe – Pretty Big Shoes |url=https://www.prettybigshoes.com/blog/shoe-widths-guide |access-date=2024-03-27 |website=www.prettybigshoes.com |language=en}}</ref>
!N-M-R-W
system
!North American
system
!North American
variant
!UK
system
!German
system
|-
|SS (super slim)
|AAAA
|4A
|
|
|-
|S (slim)
|AAA
|3A
|
|
|-
|N (narrow)
|AA
|2A
|B ("narrow")
|E ("very slim")
|-
|N (narrow)
|A
|A
|C
|E
|-
|M (medium)
|B
|B
|D ("Standard")
|F ("slim")
|-
|M (medium)
|C
|C
|D
|F
|-
|R (regular)
|D
|D
|D
|F
|-
|W (wide)
|E
|E
|E ("Wide")
|G ("comfort")
|-
|XW/EW (extra wide) / WW (wide wide)
|EE
|2E
|EE
|H ("strong")
|-
|UW (ultra wide) / WWW
|EEE
|3E
|EEE
|J ("super wide")
|-
|UW (ultra wide) / WWW
|EEEE
|4E
|
|K
|-
|XXW (extra extra wide)
|EEEEE
|5E
|
|L
|-
|XXW (extra extra wide)
|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<ref name="orthopedic" /> 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 (and actually too long) 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.<ref name="brannock2" />

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 [[#ISO 19407 and shoe size conversion|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.<ref name=":0" /><ref>{{Cite news|url=https://www.blitzresults.com/en/shoe-size/|title=Shoe Size Conversion: Use this EASY Tool, Size Guide + How To|date=2017-11-11|work=BlitzResults.com|access-date=2018-06-22|language=en-US}}</ref>