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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 of them 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 (or 1) is positioned. Some systems also indicate the shoe width, sometimes also as a number, but in many cases by one of more letters. Additionally, some regions use different shoe-size systems for different types of shoes (e.g., men's, women's, children's, sport, or safety shoes).
The length of a "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 of the foot is measured with the subject standing barefoot and the weight of the body equally distributed on 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 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.
A shoe-size system can refer to three characteristic lengths:
All these measures differ substantially from one another for the same shoe.
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 sizing systems also place size 0 (or 1) at different locations:
Some systems also include the width of a foot, but do so in a variety of ways:
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 3⁄16 inch.
The International Standard is ISO 9407:1991, "Shoe sizes—Mondopoint system of sizing and marking", which recommends a shoe-size system known as Mondopoint.
It is based on the mean foot length and width for which the shoe is suitable, measured in millimetres. A shoe size of 280/110 indicates a mean foot length of 280 millimetres (11 in) and width of 110 millimetres (4.3 in).
Because Mondopoint also takes the foot width into account, it allows for better fitting than most other systems. It is, therefore, used by "NATO and other military services. Mondopoint is also used for ski boots.
Shoe size in the "United Kingdom and "Ireland is based on the length of the "last used to make the shoes, measured in "barleycorn ( 1⁄3 inch) starting from the smallest size deemed practical, which is called size zero. It is not formally standardised. Note that the last is typically longer than the foot heel to toe length by about 1/2 to ⅔ inch (13 to 17 mm).
A child's size zero is equivalent to 4 inches (a "hand = 12 barleycorns = 10.16 cm), and the sizes go up to size 13 1⁄2 ( 8 1⁄2 in, 25 1⁄2 barleycorns or 21.59 cm). Thus, the calculation for a children’s shoe size in the UK is:
An adult size one is then the next size up ( 8 2⁄3 in or 22.01 cm) and each size up continues the progression in barleycorns. The calculation for an adult shoe size in the UK is thus:
Note: some manufacturers choose to use a constant other than 25, so sizes do vary in either direction e.g. A shoe marked as a European size 40 may also be marked as a UK: 6 by Jimmy Choo, Nike; a 6 1⁄2 by Adidas, Clarks, Dr Martens, Fred Perry, "Karrimor, Monsoon, New Balance, "Reebok, and "Slazenger; a 7 by Converse, Gap, Pavers, and Timberland; and a 7 1⁄2 by Crocs.
For men and children's footwear the UK system is followed. Women's footwear has a slightly different sizing that is unique. It is in between the UK and US's sizings.["citation needed]
In North America, there are different systems that are used concurrently. The size indications are usually similar but not exactly equivalent especially with athletic shoes at extreme sizes.
The traditional system is similar to English sizes but start counting at one rather than zero, so equivalent sizes are one greater. This is similar to the way that floors in buildings are numbered; the British count the ground floor as zero, whereas the Americans count the ground floor as one.
So the calculation for a male shoe size in the USA or Canada is:
Women's sizes are almost always determined with the "common" scale, in which women's sizes are equal to men's sizes plus 1.5 (for example, a men's 10.5 is a women's 12). In other words:
In the less popular scale, known as the "standard" or "FIA" (Footwear Industries of America) scale, women's sizes are men's sizes plus 1 (so a men's 10.5 is a women's 11.5).
Children's sizes are equal to men's sizes plus 12 1⁄3. Children’s sizes do not differ by gender even though adults’ do.
Children's shoe stores in the United States and Canada use a sizing scheme which ends at 13, after which the adult range starts at 1:
Alternatively, a scale running from K4 to K13 and then 1 to 7 is in use. K4 to K9 are "toddler sizes, K10 to 3 are "pre-school and 1 to 7 are "grade school sizes.
A slightly different sizing method is based on the "Brannock Device, a measuring instrument invented by "Charles F. Brannock in 1925 and now found in many shoe stores. The formula used by the Brannock device assumes a foot length ⅔ inch (1.7 cm) less than the length of the last; thus, men's size 1 is equivalent to a foot's length of 7 ⅔ inches. Women's sizes are one size up.
The method also measures the length of the distance of the heel and the widest point of the foot. For that purpose, the device has another, shorter scale at the side of the foot. If this scale indicates a larger size, it is taken in place of the foot's length.
For children's sizes, additional wiggle room is added to allow for growth.
The device also measures the width of the foot and assigns it designations of AAA, AA, A, B, C, D, E, EE, or EEE. The widths are 3/16 in apart and differ by shoe length.
Some shoe stores use optical devices to precisely measure the length and width of both feet and recommend the appropriate shoe model and size. 
The Continental European system is used in "France, "Germany, "Italy, "Spain, and most other continental European countries. It is also used in Middle Eastern countries (like "Iran), "Brazil—which uses the same method but subtracts 2 from the final result—["citation needed] and, commonly, "Hong Kong.
In this system, the shoe size is the length of the "last, expressed in "Paris points, for both sexes and for adults and children alike. Because a Paris point is ⅔ of a centimetre, the formula is as follows:
To compute the size based on actual foot length, one must first add a length of about 1.5 to 2 cm. For instance, for a shoe having an internal length 1.5 cm longer than the foot:
The Asian system is based on metric measurements and standardised as "JIS S 5037:1998, CNS 4800, S 1093, or KS M 6681. Foot length and girth are taken into account.
The foot length is indicated in centimetres; an increment of 5 mm is used. This system was also used in the "GDR.
The length is followed by designators for girth (A, B, C, D, E, EE, EEE, EEEE, F, G), which is taken from a table indexed to girth and length. There are different tables for men's, women's, and children's (less than 12 years of age) shoes. The tables also include the width as supplemental indications. Not all designators are used for all genders and in all countries. For example, the largest girth for women in China is EEEE, whereas in Japan, it is F.
Shoes are sized either according to the foot length they are intended to fit, in cm, or alternatively to another variation of the barleycorn system, with sizes calculated approximately as:
Historically the USSR used the European (Paris point) system but an alternate metric system (State Standard 3927–64) was devised, with shoe sizes increasing in ½ rather than the ⅔ cm intervals found in the European scheme. This system has been refined by later standards:
Where used this system is sometimes described as a Pointe (ballet shoe) or Stych size:
|Foot Length (mm)||105||110||115||120||125||130||135||140||145||150||155||160||165||170||175||180||185||190||195||200||205||210||215||220||225||230||235||240||245||250||255||260||265||270||275||280||285||290||295||300||305||310||315|
Please note that the following tables indicate theoretical sizes calculated from the standards and information given above. Differences between various shoe size tables, makers' tables or other tables found on the Web are usually due to the following factors:
Further, some tables available on the Web simply contain errors. For example, the wiggle room or different zero point is not taken into account, or tables based on different U.S. systems (traditional and athletic) are simply combined although they are incompatible.