Free size chart JSON API
Every conversion table on MySizeCharts is available as static JSON. No API key, no rate limit, no sign up. Just fetch the file and build on it.
Endpoints
All endpoints are static JSON files served from the CDN, so they are fast and cacheable. Each file includes a small metadata block (source, license, last updated) alongside the data arrays.
| Endpoint | Description |
|---|---|
/api/index.json | Index of every endpoint. |
/api/ring-sizes.json | Ring sizes: US, UK, EU, JP, diameter and circumference in mm. |
/api/shoe-sizes.json | Shoe sizes: adult (US M, US W, UK, EU, cm) and kids. |
/api/bra-sizes.json | Bra bands and cups across US, UK, EU, FR, IT, AU. |
/api/hat-sizes.json | Hat sizes: US, UK, EU, letter and head circumference. |
/api/clothing-sizes.json | Clothing: women, men and youth across US, UK, EU, IT, FR. |
/api/glove-sizes.json | Glove sizes by hand circumference. |
/api/belt-sizes.json | Belt sizes by waist and belt length. |
/api/sock-sizes.json | Sock sizes mapped to shoe ranges. |
Example
Fetch a table and read a conversion in a few lines of JavaScript:
// Fetch the ring size table
const res = await fetch("https://mysizecharts.com/api/ring-sizes.json");
const data = await res.json();
// data.sizes is an array of rows:
// { us, uk, eu, jp, diameterMm, circumferenceMm }
const usSeven = data.sizes.find((r) => r.us === "7");
console.log(usSeven.uk); // "N"License and attribution
The data is published under CC BY 4.0, stated as a machine-readable license field in every file. Free to use, including commercially. All the licence asks for is the attribution: a link back to MySizeChartswhere the data is shown. The tables are anchored to a physical measurement and, where one exists, a named published standard, which you can read in full on the methodology page. Sizing is still a guide, so validate against a specific brand where fit is critical.
Versioning and stability
Every file carries a version and a lastUpdated field, so you can detect a change without diffing the payload. lastUpdated is the date the data actually changed, taken from version control, not the date of the last deploy.
The current shape is pinned at /api/v1/ as well as the unversioned path. If a field ever has to change shape, the unversioned path moves and /api/v1/ keeps working, so nothing you built breaks on a Tuesday morning.
Changes are published in the changelog and as RSS at /changelog.xml. Subscribe and you will know before a field changes, without giving anyone an email address. There is no key, no account and no rate limit, and there never will be.
Every endpoint sends Access-Control-Allow-Origin: *, so it works from a browser on your own domain.
Last reviewed and updated on August 5, 2026. API data is regenerated with each site build.