Jewellers Calculator.

Carit is the jewellers calculator app built for the UK bench jeweller - ring sizes in UK letters and half-letters, hallmarking standards for 9ct, 14ct, 18ct and 22ct gold, sterling silver (.925) and Britannia (.958), plus every other bench calculation you reach for daily. Built by a bench jeweller, used in workshops from Hatton Garden to Glasgow to Cardiff. Available on iOS and Android.

Built for the UK bench

UK bench jewellers have needs that US-focused tools often miss. Ring sizes work in letters (A to Z+) with half-letter steps, not quarter-number steps. Hallmark assay expects 375 / 585 / 750 / 916 fineness marks for 9ct, 14ct, 18ct and 22ct gold respectively. Silver hallmarks include Britannia (958), sterling (925) and the occasional 800 fineness. The UK uses millimetres for everything (gauge, mandrel, mm stone sizes), pounds sterling for pricing, and troy ounces for precious metal weights at the dealer level.

Carit defaults to UK conventions when you set the locale to English (UK). Every calculator respects the UK terminology and measurement conventions your workshop already uses.

Every calculator inside Carit

This page is the UK bench jeweller's overview. Each calculator has its own dedicated documentation page - follow the links for the deep detail.

UK hallmark standards Carit supports

UK hallmarking is among the most rigorous in the world. The London, Birmingham, Sheffield and Edinburgh Assay Offices all test to the same purity thresholds. Carit's calculations respect these standards so your quoted metal purity matches the assay mark.

Note that 9ct gold - relatively rare in the US but extremely common in the UK - is a first-class citizen in Carit. The specific gravity (10.90 g/cm³), alloy recipes, and hallmark identity all resolve correctly.

UK ring size conventions

UK ring sizes use single-letter codes from A (very small) through Z+ (very large), with half sizes written as L½, M½ etc. The step between each whole letter is approximately 0.4 mm of inner diameter. The most common UK women's size is N (16.9 mm inner diameter, approximately 53.1 mm circumference), which converts to approximately US 6½. The most common UK men's size is T (19.7 mm inner diameter, ≈ 61.9 mm circumference, US 10).

Carit's ring sizer handles all UK letter and half-letter sizes plus conversion to US, EU and Japan. Full detail: ring size calculator →

Live metal prices in GBP

Carit pulls live gold, silver, platinum and palladium spot prices and lets you view them in your chosen currency, including GBP. For UK jewellers this means every casting, every ring weight and every quote multiplies through today's spot in pounds sterling - not a stale weekly figure off a chart, and not a dollar price you have to convert manually.

Live pricing is a Carit Pro feature. The conversions and calculators themselves are free in the base app.

Who uses Carit in the UK jewellery trade?

Carit is used by bench jewellers across the UK trade: Hatton Garden setters and remount workshops, Birmingham Jewellery Quarter goldsmiths, Sheffield silversmithing workshops, Edinburgh hallmark-submitting studios, Glasgow designer-makers, and independent bench jewellers working from home studios the length of the country. Also by jewellery students at Central Saint Martins, Birmingham City University, Glasgow School of Art, and every other major UK jewellery programme.

If you're outside the UK

If you prefer US spelling and US conventions (quarter-sizes, karat abbreviated K rather than ct), see the US-spelling version: jeweler calculator (US). Both are the same tool documented with regional context. The app itself supports 27 languages and all four ring-size systems.

FAQ