# Shoe Size Converter

> Converts an adult shoe size between US men's, US women's, UK, EU (Paris point) and centimetre foot-length (Japanese / Mondopoint) sizing with the adult formulas of the Wikipedia 'Shoe size' article, snapping to the nearest half UK size of the adult chart (UK 3–14).

- Calculator id: `shoe-size` · Category: Everyday Life (`everyday`) · Tool name: `convert_shoe_size`
- Canonical page: https://tttkmbb.com/everyday/shoe-size · This document: https://tttkmbb.com/everyday/shoe-size.md · JSON definition: https://tttkmbb.com/everyday/shoe-size.json

## Purpose

Converts an adult shoe size between US men's, US women's, UK, EU (Paris point) and centimetre foot-length (Japanese / Mondopoint) sizing with the adult formulas of the Wikipedia 'Shoe size' article, snapping to the nearest half UK size of the adult chart (UK 3–14).

**Use when:** You have a shoe size in one system, or a measured foot length in centimetres, and need the equivalent adult US, UK, EU or centimetre size.

**Do not use when:** You need children's sizes (different scales), width fittings, or an exact match for a specific brand — brand charts differ by up to a full size, so use the brand's own table; to convert foot lengths between units use length.

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `size` | number |  | required | The size number in the chosen system (for cm: the measured foot length in centimetres). (min 0, max 60) |
| `system` | enum: us_men \| us_women \| uk \| eu \| cm |  | required | System of the entered size. |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `us_men` | number |  | US men's size = UK + 1. |
| `us_women` | number |  | US women's size = US men's + 1.5 (common retail scale; athletic/FIA charts use +1). |
| `uk` | number |  | UK size, the nearest half size of the adult chart (3–14). |
| `eu` | number |  | EU (Paris point) size = 1.5 × foot length in cm + 2, rounded to the nearest half size. |
| `cm` | number | cm | Foot length of the chart row, (UK + 23) / 3 inches in cm; the basis of Japanese and Mondopoint sizing. |
| `jp` | number | cm | Japanese (JIS) size = foot length in cm rounded to the nearest 0.5. |
| `foot_length_in` | number | in | Foot length of the chart row in inches. |
| `note` | string |  | Chart row used and the brand-variation caveat. |

## Formula

`foot_in = (UK + 23) / 3 = (US_men + 22) / 3 = (US_women + 20.5) / 3; cm = foot_in × 2.54 = (EU − 2) / 1.5; UK = 3 × foot_in − 23 rounded to the nearest 0.5 (chart UK 3–14); US_men = UK + 1; US_women = US_men + 1.5; EU = 1.5 × cm + 2 rounded to the nearest 0.5; JP = cm rounded to the nearest 0.5`

Adult formulas from the Wikipedia 'Shoe size' article: the UK/US barleycorn scale (1/3 inch per size, US men's one size above UK) and the EU Paris point (2/3 cm per size, including the 2-point last allowance). The result is the chart row nearest to the input, so converting back and forth can move by half a size; manufacturers' charts deviate by up to one full size and their cm/Japanese labels typically run 0.5–1 cm larger than the measured foot.

## Data Sources

- Shoe size – sizing systems and adult conversion formulas (Wikipedia) — https://en.wikipedia.org/wiki/Shoe_size (reference, retrieved 2026-09-24)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/shoe-size?size=…&system=…`
- `POST https://tttkmbb.com/api/v1/calculate/shoe-size` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/shoe-size · OpenAPI operationId `convert_shoe_size` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool:  `run_calculator` with `{"calculator_id": "shoe-size", "inputs": {…}}`

## Example

- US men's 10: inputs `{"size":10,"system":"us_men"}` → `{"us_men":10,"us_women":11.5,"uk":9,"eu":42.5,"cm":27.1,"jp":27,"foot_length_in":10.67}`
- 24 cm foot length: inputs `{"size":24,"system":"cm"}` → `{"uk":5.5,"us_men":6.5,"us_women":8,"eu":38,"cm":24.1,"jp":24}`

```
GET https://tttkmbb.com/api/v1/calculate/shoe-size?size=10&system=us_men
```

## Limitations

You need children's sizes (different scales), width fittings, or an exact match for a specific brand — brand charts differ by up to a full size, so use the brand's own table; to convert foot lengths between units use length. Adult formulas from the Wikipedia 'Shoe size' article: the UK/US barleycorn scale (1/3 inch per size, US men's one size above UK) and the EU Paris point (2/3 cm per size, including the 2-point last allowance). The result is the chart row nearest to the input, so converting back and forth can move by half a size; manufacturers' charts deviate by up to one full size and their cm/Japanese labels typically run 0.5–1 cm larger than the measured foot. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**Why does my brand's chart give a different EU or cm size?**

Brands size on their own lasts: EU labels vary by about ±1 and cm/Japanese labels usually include 0.5–1 cm of toe room beyond the measured foot. This tool applies the published formula relations, so treat the result as a starting point.

**Which US women's scale is used?**

The common retail scale (women's = men's + 1.5). Athletic brands using the FIA scale label women's shoes only one size above men's; subtract 0.5 for those.

**How do I measure foot length?**

Stand on paper, mark the heel and the longest toe, measure the distance in cm and use the larger foot; enter it with system cm.

## Related

- [Ring Size Converter](https://tttkmbb.com/everyday/ring-size.md) — Ring sizes between US, UK, EU, Japan and millimetres.
- [Length Converter](https://tttkmbb.com/conversion/length.md) — Convert foot length between centimetres and inches.