Shoe width and girth, explained
Width is the second dimension of fit after length. This is what the width letters mean — and the exact millimetres behind them: the girth steps, the forefoot base width, and why a correctly sized shoe is built longer than your foot.
Last updated June 2026 · ARFits Editorial
In short
Shoe width is graded in letters (A narrowest → K widest) or numbers 1–12. Each width grade is a fixed millimetre step in the foot's girth (circumference), not just flat width. In the standard shoemaking width system, adjacent width grades differ by about 6 mm of girth (about 3 mm for infants), and the forefoot base width changes about 4 mm per grade. Length tells you the size; girth tells you the width letter.
What "girth" means
Width on a flat tape is only half the story. The measurements that actually define a width grade are girths — circumferences taken all the way around the foot. Two girths matter:
Ball / forefoot girth
The circumference around the joints of the big toe and little toe — over the heads of the 1st and 5th metatarsals. This is the widest functional part of the foot, and the single most important girth for fit.
Instep / waist girth
The circumference at the mid-foot, taken over the first cuneiform bone and the bump of the 5th metatarsal. It captures the volume of the arch and how high the foot sits inside the shoe.
Two feet of equal length can need different widths because their girth differs. This is exactly why a length-only size chart mis-fits wide or narrow feet — and why a foot scan that captures ball girth is more reliable than a number read off a length table.
The width letter system
Width grades run from A (narrowest) to K (widest), with equivalent numbers 1–12. The marking colours below are a documented trade convention used to identify a last or shoe's width on the factory floor.
| Letter | Number | Typical use | Marking colour (where used) |
|---|---|---|---|
| A | 1 | Narrowest. Slimmer feet — common in Italy, the UK, the USA. | Unmarked |
| B | 2 | Slimmer feet — common in Italy, the UK, the USA. | Unmarked |
| C | 3 | Slimmer feet — common in Italy, the UK, the USA. | Unmarked |
| D | 4 | Slimmer feet — common in Italy, the UK, the USA. | Unmarked |
| E | 5 | Common European range. | Black |
| F | 6 | Common European range. | Yellow |
| G | 7 | Common European range. | Red |
| H | 8 | Common European range; typical for work and sport footwear. | Green |
| CH | 9 | Common European range; typical for work and sport footwear. | Violet |
| I | 10 | Common European range; typical for work and sport footwear. | Unmarked |
| J | 11 | Special / military footwear. | Unmarked |
| K | 12 | Widest. Special / military footwear. | Unmarked |
A–D suit slimmer feet and are common in Italy, the UK and the USA; E, F, G, H, CH and I make up the common European range. H, CH and I are typical for work and sport footwear, while J and K are reserved for special and military footwear. Marking colours (E = black, F = yellow, G = red, H = green, CH = violet) are a trade convention; A–D and I–K are typically left unmarked.
The millimetres behind a width grade
A width grade is not a vague "wide" — it is a defined set of millimetre steps. Moving one grade wider changes several measurements at once:
- •≈6 mm of girth between adjacent width grades (about 3 mm for infant sizing). This girth step is the primary thing a width letter encodes.
- •≈4 mm of forefoot base width between adjacent grades — the flat across-the-ball measurement of the last's tread.
- •≈1.3 mm of heel base width per grade across the common range. The heel changes far less than the forefoot, because most width difference lives at the ball.
A single width grade has four defining measurements
Each grade is fully specified by forefoot base width, heel base width, instep girth, and ball / forefoot girth. Together these four numbers — two flat widths and two circumferences — are what make one grade reliably distinguishable from the next.
Why a shoe is longer than your foot
The last — the foot-shaped mould a shoe is built on — is deliberately longer than the foot. It carries a built-in functional allowance at the toe of about 15 mm in the classic German last-construction method (Forschungsstelle für Leisten und Schuhbau). That allowance gives the toes room to splay and the foot room to slide forward as you walk, without the toe touching the front of the shoe.
The last's length is also split front-to-back at the tread (ball) line into a major part of about 62% and a minor part of about 38%. This proportion places the widest point of the shoe under the ball of the foot, where the foot is actually widest. The toe allowance is the structural reason a correctly sized shoe measures longer than the bare foot — and it is separate from the per-size length step that distinguishes one size number from the next.
How this maps to size systems
Width is independent of the length number. The same EU, UK or US length can be produced in several widths — a single size number does not pin down the fit on its own. The length system tells you which size to start from; the width grade then adjusts the girth around your foot to match.
Frequently asked questions
What do shoe width letters like D, E, or G mean?
They are width grades — a measure of how wide the shoe is at a given length, expressed as a letter (A narrowest to K widest) or the equivalent number (1–12). A–D suit slimmer feet and are common in Italy, the UK and the USA; E, F, G, H, CH and I are the common European range. Each letter is a fixed step in the foot's girth, not just flat width: adjacent grades differ by about 6 mm of girth.
How much wider is each width grade?
In the standard shoemaking width system, each adjacent width grade differs by about 6 mm of foot girth (about 3 mm for infant sizing) and about 4 mm of forefoot base width. The heel base width changes about 1.3 mm per grade across the common range.
What is the difference between width and girth?
Width is a flat side-to-side measurement; girth is the circumference all the way around the foot. Width grades are defined primarily by girth — ball (forefoot) girth around the joints of the big and little toes, and instep (waist) girth across the mid-foot. Because girth captures the volume of the foot, two feet with the same flat width can still need different width grades.
Why is a shoe longer than my foot?
Because the last — the foot-shaped mould a shoe is built on — is deliberately made longer than the foot. In the classic German last-construction method there is a built-in functional allowance at the toe of about 15 mm. This toe allowance is the structural reason a correctly sized shoe measures longer than the bare foot, separate from the per-size length step.
Can two feet of the same length need different sizes?
Yes. Length sets the size number, but girth sets the width grade. Two feet of identical length can have different ball and instep girth, so one may need a wider width grade than the other. This is exactly why a length-only size chart mis-fits wide or narrow feet.