TL;DR: carat measures the weight of a diamond or gemstone, and karat measures how pure a piece of gold is. They sound alike and in British English are even spelled alike, but they are completely different things. A two carat diamond has nothing to do with eighteen karat gold. Knowing which is which stops you misreading a description. Pieces start from £600.
Carat: weight
A carat is a unit of weight for gemstones. One carat is a fifth of a gram. A larger carat weight usually means a larger stone, but shape, cut and proportions change how big a stone looks. See our guide to the diamond clarity scale for another part of diamond grading.
Karat: gold purity
Gold purity is measured out of twenty four parts. Pure gold is twenty four karat. Eighteen karat gold is eighteen parts gold in twenty four, with other metals making up the rest. Fewer parts of gold make the metal harder and often paler or redder, depending on the alloy.
The spelling in the UK and US
In American English, carat is used for stones and karat for gold. In British English, you will often see carat used for both, which is where the confusion comes from. We try to be clear in context. For example, we write a one carat diamond, and eighteen carat gold.
How to read a description
- A 1.50 carat diamond means the stone weighs one and a half carats.
- 18ct gold means 75 percent pure gold.
- 9ct gold means just over a third gold, and 14 karat gold means a little under 60 percent.
- Platinum is described by a purity figure out of a thousand, not by karat.
A worked example
Imagine a description that reads one carat diamond in 18ct yellow gold. The first carat is the weight of the stone, which is about a fifth of a gram. The second is the purity of the gold, 18 parts in 24. They describe two separate parts of the ring. A common mistake is to think the ring is two carats in total, which is not what the description says.
Total carat weight
When a ring has more than one stone, such as a halo or a three stone design, you may see a total carat weight. That figure adds up every stone in the piece, so a ring described by its total weight may have a much smaller centre stone than the number suggests. Ask for the weight of the centre stone on its own, and for its measurements, so you know exactly what you are comparing.
Why gold purity matters
Higher purity gold is softer and more yellow. Lower purity gold is harder, which can help with daily wear. We state the metal and purity in writing for every design. Our guide to polishing or replating explains care.
Gold colours
Yellow, white and rose gold get their colours from the metals mixed with the gold. That is why the same purity can look different. Ask us to show you samples on video, and we explain how each colour wears.
Where hallmarks come in
In the UK, precious metal items are hallmarked to show the metal and purity. See our guide to UK hallmarking and our note on inherited ring hallmarks and wear.
Working with us
We work by video consultation and message, send sketches and CAD renders, and make nothing until you approve the design in writing. Standard making time is 5 to 6 weeks, varying with your location and how busy we are. Overseas, the customer pays import duty and tax, and delivery is insured and tracked with FedEx.
Frequently asked questions
Is carat the same as karat?
No. One is weight, the other is gold purity.
Is 18ct gold better than 9ct?
It is purer. Which suits you depends on wear.
Does a bigger carat always mean a bigger stone?
Usually, but cut matters.
Can I choose the gold purity?
Yes, and we explain the options.
What does total carat weight mean?
It is the combined weight of every stone in a piece, not just the centre stone.