There are several ISO standards related to Size designation of clothes.
ISO 3635:1981 Size designation of clothes -- Definitions and body measurement procedure
ISO 4416:1981 Size designation of clothes -- Women's and girls' underwear, nightwear, foundation garments and shirts
ISO 5971:1981 Size designation of clothes -- Pantyhose
ISO 8559:1989 Garment construction and anthropometric surveys -- Body dimensions
ISO/TR 10652:1991 Standard sizing systems for clothes
The European Union has produced a standard EN 13402 intended to replace existing standards in the member countries. This is not yet in common use.
The United Kingdom has an existing standard for women's clothing BS 3666:1982, however this is rarely followed by manufacturers as it defines sizes in terms of hip and bust measurements only within a limited range. See table of sizes. This has resulted in variations between manufacturers and a tendency towards vanity sizing.
The standard sizes have not had stable names, however. For example, the dimensions of two size 10 dresses from different companies, or even from the same company, may have grossly different dimensions; and both are almost certainly larger than the size 10 dimensions described in the US standard. Vanity sizing may be partly responsible for this deviation (which began in earnest in the 1980s).
The new European standard EN 13402 seeks to address this problem, since it is an absolute scale and mandatory; there is no mandatory clothing size standard in the U.S. In the US there exists a US standard clothing size.
 Women

Women's Dresses and Suits
United States 0 2 4 6 8 10 12 14 16 18 20
Italy 36 38 40 42 44 46 48 50 52 54 56
Scandinavia and Germany 30 32 34 36 38 40 42 44 46 48 50
France, Spain and Portugal 32 34 36 38 40 42 44 46 48 50 52
UK and ROI 4 6 8 10 12 14 16 18 20 22 24
Japan 3 5 7 9 11 13 15 17 19 21 23

Women’s blouses and sweaters
EU 40 42 44 46 48 50
UK 34 36 38 40 42 44
US 32 34 36 38 40 42

Children’s junior misses dresses and coats
EU 28 30 32 34 36 38 40 42
UK 3 5 7 9 11 13 15 17
US 1 3 5 7 9 11 13 15

Men

Men’s suits, sweaters, overcoats
EU 46 48 50 52 54 56 58 60 62
UK / US 36 38 40 42 44 46 48 50 52

Men’s shirts
EU 37 38 39 40 41 42 43
UK / US 14½ 15 15½ 15¾ 16¼ 16½ 17