How Do Shoe Sizes Work Across Countries?

There is no international standard for shoe sizes, which is the root of every problem with them. Four major systems exist, they measure different things, and the conversion tables that claim to reconcile them disagree with each other by up to a full size.

The UK system

Based on the barleycorn, an old English unit of one third of an inch. Adult sizing starts at a nominal foot length and each size adds a barleycorn, so each full size is 8.47 mm longer than the last and each half size is about 4.2 mm.

Child sizes run 0 to 13 and then restart at adult 1, which is why a child 13 and an adult 1 sit next to each other rather than being twelve sizes apart.

The US system

Uses the same barleycorn increment but starts from a different point, so US sizes run higher than UK ones for the same foot.

For men, a US size is roughly one size above the UK. For women, the offset is closer to two. This is why conversion tables show a men’s UK 9 as a US 10 but a women’s UK 6 as a US 8.

The United States also splits men’s and women’s sizing with an offset of about one and a half sizes between them, so a women’s 8 is roughly a men’s 6.5.

The European system

Uses the Paris point, which is two thirds of a centimetre, so each full size is 6.67 mm. There are no half sizes in the original system, though some manufacturers add them.

Crucially, European sizing does not distinguish between men’s and women’s sizes. The number is the same on both charts, which is why EU sizing is often the easiest to shop across.

It also measures the length of the last rather than the foot, and includes an allowance for toe room that varies by manufacturer.

The Japanese system

The simplest and most honest of the four. The size is the foot length in centimetres, usually in half-centimetre steps.

A 26 means a 26 cm foot. No conversion, no offset, no gender split. It is the only one of the four systems where the number on the box describes your foot rather than the mould the shoe was made on.

Why conversions disagree

Three reasons, all structural.

Different increments. UK and US sizes step by 8.47 mm, European by 6.67 mm. The two scales cannot align neatly, so conversions round in different directions at different points.

Different starting points. Each system defines size zero differently, and the offsets between them are conventions rather than definitions.

Last length, not foot length. With the exception of the Japanese system, sizes describe the mould, which includes an allowance for toe space. Manufacturers choose that allowance, so two identically sized shoes can fit differently even within one system.

This is why published conversion tables differ. They are all approximations of a relationship that is not exact.

The measurement that always works

Measure your foot and work in centimetres.

1. Stand on a sheet of paper with your heel against a wall.
2. Mark the end of your longest toe, which is not always the big toe.
3. Measure from the wall to the mark.
4. Do both feet. They frequently differ by several millimetres, and you size to the larger one.
5. Measure in the afternoon or evening, since feet swell during the day by a noticeable amount.

Then use the brand’s own size chart, which almost every manufacturer publishes in centimetres, rather than a generic conversion.

Width, which the number ignores

Length is only half of fit. Most systems have width fittings, usually lettered, and most high-street shoes are only made in one or two of them.

Someone with a wide foot buying a longer shoe to get width ends up with a shoe that is too long and still too narrow. If shoes routinely feel tight across the ball of the foot while the length is right, the answer is a wider fitting rather than a larger size.

Practical guidance

• Leave about a centimetre between your longest toe and the end of the shoe when standing.
• Expect variation between brands of up to a full size, and between models within a brand.
• Size up for running shoes, often by half a size, because feet swell during exercise.
• Trust the brand chart over a conversion table, always.
• Check the return policy when buying online, because even with correct measurements, fit is not fully predictable.

Why the systems survive

Each is entrenched in a manufacturing base with its own tooling, and lasts are expensive to retool. There have been attempts at an international standard based directly on foot length in millimetres, and it has never displaced the incumbents.

So the practical answer is not to learn the conversions but to stop relying on them. Know your foot length in centimetres and treat every size number as a brand-specific approximation of it.