Free size chart JSON API
Every conversion table on SizeCharts 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 free to use, including commercially. All we ask is a link back to SizeCharts where the data is shown, so your users can find the full reference and so the project keeps improving. The tables are checked against published international sizing standards, but sizing is a guide, so validate against a specific brand where fit is critical.
Stability
Endpoint paths and field names are stable. When tables are corrected, the change is noted in the changelog and the updated date in each file changes. We will not rename fields without a heads up on the changelog.
Last reviewed and updated on July 2, 2026. API data is regenerated with each site build.