Size Conversion API

International size conversion as an API, for the everyday wearables that ship in different scales around the world. The shoe endpoint converts a shoe size between EU (Paris point), UK, US men, US women, Mondopoint and foot length in centimetres — derived from the standard barleycorn and Paris-point relationships — and reports both the exact figure and the nearest standard half-size. The ring endpoint converts a ring size between US numeric, ISO 8653 (inside circumference in millimetres, used across most of Europe), inside diameter, inside circumference and the UK alphabetical scale. The hat endpoint converts a hat size between head circumference (centimetres or inches), the EU metric size, US and UK, with a simple S/M/L band. Everything is computed locally and deterministically, so it is instant and private. Ideal for fashion and footwear e-commerce, jewellery shops, size-guide widgets, returns-reduction tooling and international checkout. Pure local computation — no key, no third-party service, instant. Live, nothing stored. Guidance only — manufacturers' sizing varies, so always check the brand's own chart for a critical fit. 3 endpoints. This is wearable-size conversion; for plain length/weight unit conversion use a unit-conversion API.