The bench jeweller's
calculator hub.

Every jewellery calculator you actually reach for at the bench, one page per tool. Ring sizing, metal weight, alloy mixing, diamond setting, stone weight, eternity layouts - all built by a working bench jeweller, all inside the Carit app on iOS and Android. The pages below explain how each calculator works, the formulas behind it, and the reference data it uses.

Every calculator, one page.

A bench jeweller reaches for the same handful of calculations every single working day. What size is a UK M in US? How much 18k white gold do I need for this wax? How many 1.2 mm stones fit around a size 7 band? What's the carat weight of a 4.5 mm round brilliant? Each one of those questions has an exact answer, and each one lives inside the Carit app.

The pages below document each calculator individually - what it does, how it works, the formulas it uses, and the reference data behind it. Pick the one you'd reach for tomorrow to see how Carit handles it.

What makes a good jewellery calculator?

Most "jewellery calculators" on the web are one of two things: a cash-for-gold value calculator aimed at consumers who want to sell scrap, or a Google-Play .apk listing that sends you to an Android app with a 2013 UI. Neither serves a working bench jeweller. What you actually need is different, and it comes down to four things.

1. Intent matching

When you type "goldsmith calculator" you don't want a page about goldsmithing. You want a calculator, open, working, with your number field already focused. Every page on Carit's hub has its calculator at the top - usable without scrolling, usable without signing up, usable on mobile with wax on your hands.

2. Correct formulas

There are cached ring-size charts online that disagree with each other by a full UK letter. There are "gold weight" calculators that silently assume 18k yellow and break on rose. There are stone-weight calculators that use the old Arem formula for round brilliants but forget that marquise and pear have entirely different factors. Every Carit calculator uses the industry-standard formulas you'd find in a GIA reference - specific gravities cross-checked against Stuller and Rio Grande charts, ring-size tables anchored to circumference in millimetres rather than inherited letter codes, stone factors sourced from the published carat-weight formulas used by every major lab.

3. Every metal, every size, every shape

Carit supports 20+ alloys (9k through 24k gold in yellow / white / rose, platinum 950, palladium 950, sterling, fine silver, brass, bronze, copper, titanium, stainless, tungsten), 4 ring-size systems (US in quarters, UK in half-letters, EU in millimetres, Japan whole numbers), and 11 diamond shapes (round brilliant, princess, oval, cushion, emerald, pear, marquise, asscher, radiant, heart, trillion). No hunting through multiple tools.

4. Built by someone who uses it

Every calculator on this site was built because Ian Barnard - a working bench jeweller specialising in micro diamond setting - was annoyed by the existing options. The eternity-ring stone-spacing calculator exists because he was mentally rounding 3.14 × diameter ÷ stone width seven times a week. The alloy mixer exists because most ones online silently ignore the rose-gold copper contribution. The TCW counter exists because adding up 42 melee stones in your head every time you submit a quote is absurd.

Who uses these calculators?

If any of the descriptions below sound familiar, you're in the right place.

• Bench jewellers sizing, casting, and setting at volume. You don't have time to keep reaching for a paper chart.
• Goldsmiths and silversmiths working with multiple karats and alloys. You need a weight calc that actually knows the difference between 18k rose and 18k yellow.
• Diamond setters and stone-setters planning eternity bands, pavé layouts, and multi-stone compositions. You need stone spacing that respects the real geometry of a curved band.
• Jewellery students learning to cost their work. You need formulas you can trust until they're muscle memory.
• Independent jewellery designers quoting a client over email. You need numbers you can defend in front of a customer.
• Retail jewellers and repair techs sizing rings and estimating casting weight for a remake. You need quick, accurate, same-day numbers.
• Hobby and DIY jewellery makers who've moved past beginner tutorials. You're ready for professional-grade tools without professional-grade price tags.

The app is where this actually lives.

The calculators on this site are the free web versions of what's inside the Carit iOS and Android app. If you're using them more than once a week, the app is worth it - for three reasons that matter at the bench:

1. Offline. The app works in your workshop whether or not the Wi-Fi reaches. Web calcs don't.
2. Live metal prices. Gold, silver, platinum and palladium pulled live and cached, so your quotes reflect today's market, not last week's.
3. Quote builder. Generate a professional, line-itemised quote from the same calculators that sized the ring and weighed the metal, then export it straight to the client.

Frequently asked questions