Development guide

Shoe Sizing, Lasts & Size Grading Explained

By DOING SHOES · Reviewed by Zhu Dangli, Technical Group Leader (20 years in footwear) · Last updated 2026-08-05 · 14 min read

How footwear fit is actually decided — the last, size grading, US/EU/UK conversion, fit samples and the sizing mistakes that cause returns. A factory-side guide for brands and importers.

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Fit is the reason shoes get returned. Not colour, not materials — fit. And fit is not decided by the number printed on the box; it is decided by the last, by how that last is graded across a size run, and by which size system you produce in. Get those three right and a size 42 feels like a size 42 in every pair; get them wrong and you will be paying for returns on a shoe that passed every material test.

This guide explains how sizing actually works inside a footwear factory, so you can specify it instead of hoping.

It is written from inside a working factory. DOING has manufactured footwear since 2002, runs 4 production lines and a team of 589, produces 200,000+ pairs a month, and holds amfori BSCI and HBI (Hanesbrands) audit reports. We develop on customer lasts, on our own, and on modified versions of either.

The last is the product; the size is a label

A last is a solid form — traditionally wood, now usually plastic — shaped like a stylised foot. Every upper is pulled over it, every sole is built to its bottom. It carries:

• Length — what the size number refers to.
• Girth / width — the circumference at the ball of the foot. This is what most “runs narrow” complaints are actually about.
• Instep height — vertical volume over the arch; decides whether a foot slides in easily and whether laces bottom out.
• Heel volume and shape — decides heel slip, the complaint runners report most.
• Toe spring and toe box shape — how the shoe rolls, and how much room the toes get.

Two factories can both build you a “42” and produce shoes that fit nothing alike, because they used different lasts. This is why a brand’s fit is an asset: once buyers know your 42 fits them, that consistency is worth more than any single material upgrade. Our shoe last entry defines the term; this guide covers what to do about it.

Your last, our last, or a modified last

Route	When it makes sense	Trade-off
Factory’s existing last	First model, test run, tight budget or timeline	Fastest and cheapest; your fit is not unique
Modified factory last	You like the base fit but need more toe room, a lower instep or a narrower heel	Good balance; much cheaper than starting from scratch
Your own / newly developed last	The model sells repeatedly and fit is part of your brand	Highest cost and longest lead time; fully yours

All three are normal. Most brands start on route one or two and move to route three when a model earns it.

Size grading: where fit quietly breaks

Size grading is scaling one approved last and pattern across the whole size run so every size fits like the approved sample.

The trap: grading is not uniform scaling. Length, girth and volume change at different rates as feet get bigger, and half sizes are usually a length step without a proportional girth step. Multiply everything by one factor and you get a size run where the middle is perfect, the small sizes are sloppy and the large sizes pinch — or the reverse.

Two consequences buyers underestimate:

1. Grading errors do not show up in your base sample. They show up at the ends of the run — exactly the sizes you did not approve.
2. Grading has to be locked before mould making. The sole mould is machined to the graded last bottom. Change the grading afterwards and you are not adjusting a spec, you are buying new moulds. Our shoe mould cost guide explains what that actually costs.

US, EU, UK and JP: the systems do not convert cleanly

Four systems are in common use and none of them map onto each other exactly:

System	Based on	Notes for production
EU (Paris point)	Length in ⅔ cm steps	No true half sizes; one step ≈ 6.67 mm
UK	Length in ⅓ inch steps (barleycorn)	Half sizes standard; men’s and women’s start from different points
US	Derived from UK, offset	Men’s and women’s differ — a US 8 is not one shoe
JP / Mondopoint	Foot length in cm/mm	The most literal; converts to the others only approximately

Practical rules we give buyers:

• Fix one reference system for production and treat the others as printed conversions, not as separate specs.
• Confirm the conversion table in writing before samples, not after the first complaint.
• State insole length in millimetres on the tech pack. Millimetres are unambiguous; “size 42” is not. Our tech pack guide covers where to record it.

How fit gets approved, step by step

1. Agree the last — yours, ours, or a modified version, with the intended fit described in words (“roomy toe box, snug heel”) as well as numbers.
2. Build a fit sample in the base size — usually EU 42 / US 9 men’s or EU 38 / US 7 women’s, whichever matches your range.
3. Wear it. Not a desk check. Walk in it, and for sports shoes run in it. A fit sample that has never been worn has not been tested.
4. Record what to change in dimensions, not adjectives — “5 mm more instep height”, not “a bit loose over the arch”.
5. Approve the corrected sample, then apply grading.
6. Check the extremes. Build and try the smallest and largest sizes in the run before bulk.
7. Lock the last and grading, then cut sole moulds.

Steps 6 and 7 are the two most often skipped, and they are the two that cost the most to skip.

The five sizing mistakes that cause returns

1. Approving only the base size. Grading errors live at the ends of the run.
2. Specifying fit in adjectives. “Comfortable” is not a dimension; instep height in millimetres is.
3. Changing the last after tooling. The sole mould was cut to the old last bottom — that is new moulds, not a tweak.
4. Assuming US = UK + 1 for everything. Men’s and women’s US sizing differ, and half-size conventions differ by system.
5. Ignoring sock and insole thickness. A shoe approved barefoot and sold with a thick sock liner fits a size smaller in practice.

Sizing and semi-finished supply

If you buy components rather than finished pairs, sizing becomes a shared responsibility: the upper is built on one last and your assembler lasts it on another. Unless those lasts are identical, the upper will not pull cleanly and the size run will drift. This is the first of the five specs to settle in our semi-finished footwear guide — and the reason we approve an assembled sample on the destination line before bulk.

Working with DOING on fit

DOING is a trading-and-manufacturing partner: factory pricing with in-house development, QC and export. We develop on your last, on ours, or on a modified version; we grade the run and check the extremes before tooling; and we approve fit on worn samples, not photographs — backed by 4 own production lines, 589 people, 200,000+ pairs a month and amfori BSCI & HBI audits.

The most reliable way to specify fit is still the simplest: send a physical pair you already sell. We will measure the last dimensions, insole length, girth and volume and tell you what we would match and what we would improve.

Ready to start? Send us a reference pair or your tech pack and we will come back with a last recommendation, a grading plan and a quote. See also the sample development process and our factory.

Part of our footwear manufacturing guides by product type.