Shoe fit & foot-scanning glossary

These are the terms that come up most often when measuring feet and sizing footwear online. Definitions match how the terms are used elsewhere on this site.

AR foot scanning

A method that uses a phone camera and augmented reality to measure a foot and recommend a shoe size. A guided 12-step scan runs in the browser, captures foot length and ball girth to within ±2 mm of a podiatrist scan in about 30 seconds, and needs no app-store install.

Foot length

The heel-to-toe length of the foot, measured to the longest toe while standing. It is the primary input for shoe size and maps most directly to EU/US/UK sizing on a per-model basis.

Ball girth

The circumference around the widest part of the foot, at the ball. Two feet of the same length can need different sizes if one is wider, so capturing ball girth as well as length makes a size recommendation more reliable.

Instep (waist) girth

The circumference across the mid-foot, over the first cuneiform bone and the bump of the 5th metatarsal. It is one of the core fitting measurements alongside length and ball girth.

Heel girth

The diagonal circumference from the instep around the back of the heel. It affects heel slip and matters for boot construction.

Shoe width (girth grade)

The second dimension of fit after length, graded in letters (A narrowest to K widest) or numbers 1–12. Adjacent grades differ by about 6 mm of foot girth (about 3 mm for infants). See shoe width and girth for detail.

Brannock device

The metal in-store measuring tool that is the long-standing standard for measuring foot length and width, accurate to roughly ±2–3 mm. It is reliable but requires an in-person visit, so it does not help an at-home online shopper.

Shoe last

The foot-shaped mould a shoe is built around. The last determines a model's internal shape and fit, which is why the same labelled size fits differently across models and brands.

Last grading

The systematic stepping of a master last into a full size-and-width run by fixed millimetre increments (e.g. length steps per size, ~6 mm girth per width grade), so a whole size/width matrix is built from one shape.

Plantograph

A traditional measuring device: an inked box with a membrane that records a footprint (the loaded sole contact area) and the foot's outline, used to capture foot shape for lastmaking before digital scanning.

Size system (EU / UK / US)

The regional scales used to label shoe sizes — EU, UK, and US (with separate US men's and women's scales). The same foot maps to different numbers in each system, which is why conversion between them is needed.

Size conversion

Translating a shoe size from one system to another — for example EU to US or UK to cm — using a standard reference table. The values are widely accepted standards, but actual fit still varies by brand, model, last, and width. Use the shoe size converter to convert between systems.

Paris point (French shoe size)

The unit of the French/EU shoe-size system: one point equals 2/3 cm ≈ 6.67 mm of last length. It is why each EU size is that increment and the classic French scale has no half sizes. Use the shoe size converter to convert between systems.

Mondopoint

The ISO metric shoe-size system that labels a shoe by foot length in millimetres, typically in 5 mm steps. It is the most directly physical sizing system and is common for athletic and military footwear.

English shoe size (inch system)

The basis of UK and US sizes: one full size equals 1/3 inch ≈ 8.47 mm, and a half size equals 1/6 inch ≈ 4.23 mm. Because this step differs from the EU Paris point (~6.67 mm), EU and UK/US sizes do not line up by a constant offset.

True to size

A description of a brand or model whose labelled size matches the standard size for a given foot length, so no adjustment up or down is needed. Brands that run small are sized up, and brands that run large are sized down.

Half size

The increment between two whole shoe sizes, equal to about a half-size step in the reference table. A fit tool may suggest moving a half size up or down, and a fit heatmap can be recomputed instantly for the new size.

Fitting allowance

A small amount of length (about 10 mm of toe room) added to bare foot length when calculating a shoe size, so the shoe is not sized exactly to the foot. It is applied before converting a measured foot length to a base size.

Functional allowance (toe allowance)

The extra length built into a last beyond the foot so the shoe is not sized exactly to the foot — about 15 mm at the toe in the classic German last-construction method. It is the structural reason a correctly-sized shoe measures longer than the bare foot; the related Fitting allowance (~10 mm) is the consumer toe-room rule.

Fit heatmap

A visual overlay that shows where a shoe runs roomy (teal) or tight (coral) for a given foot and size. It helps a shopper see why a size is recommended, and updates when a different half size is selected.

Return rate

The share of orders that are sent back. In footwear, size is the single largest return reason at roughly 40% of returns, because sizing is not standardised and shoppers cannot try shoes on before buying online.

Conversion rate

The share of product-page visitors who go on to buy. Reported deployments of browser-based AR foot scanning see about a 30% lift in product-page conversion, because a confident size recommendation makes shoppers more likely to purchase.

Bracketing

The practice of ordering two sizes of the same shoe intending to return one. Each planned return is logged as a size return and adds cost, so accurate sizing before purchase reduces the volume that ever enters reverse logistics.

App Clip vs WebXR

The two ways a browser foot scan launches without an app-store install: on iOS an App Clip is invoked from the web, and on Android the scan runs through the WebXR API in the browser. For the shopper, both feel the same — tap, scan, get a size.