Sizing Systems Explained
Why no single international size exists, the ISO and regional standards behind the numbers, and how to read each system.
Three Ways a Garment Is Sized
There is no single international clothing size — only regional systems that each define a size differently: by body measurement, by product measurement, or by an ad-hoc code.
There is no single international clothing size. There is only a set of regional systems that each define a size differently — some by body measurement, some by product measurement, and some by a code with no relation to either. Converting between them is not arithmetic; it is looking up the row.
How sizes are defined
History of Standard Sizing
Before the early 1800s all clothing was bespoke. Makers then noticed the range of human body dimensions was fairly small for their demographic, so standard sizes emerged based on key measurements.
Then a key concept emerged: vanity sizing — brands inflate the measurements behind a given label number (or shrink the number for the same body) to make the wearer feel smaller. This is why you own a "Size 10" in one brand and a "Size 8" in another. Trim sizes drift; centimetres and inches do not.
- Horizontal torso: neck circumference, shoulder width, over-bust, full-bust, bust-point separation, under-bust (rib-cage), natural waist, upper-hip, lower-hip.
- Vertical torso: back (neck-waist) length, shoulder-waist length, bust-shoulder, bust-waist, two hip-waist lengths.
- Sleeve: under-arm & over-arm length, forearm length, wrist circumference, biceps circumference.
International Standards
Several ISO standards govern size designation, but most are being revised and replaced by parts of ISO 8559, which closely mirrors the European EN 13402.
ISO standards
European EN 13402 series
Regional / National Standards
The US published standard sizes (1958; updated 1970) but degraded them to voluntary and abolished them in 1983. Since then America has had no stable, mandatory baseline, and two "size 10" dresses can have grossly different actual dimensions due to vanity sizing.
Regional standards
The System Map
Country-to-system reference — what each region uses for womenswear and menswear.