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What is carat weight?

Custom designed ring with large diamond and cluster diamond surroundYou’ve all heard it, or said it, when a friend presents her new diamond engagement ring: ‘how many carats is it?’  and then we breathlessly hang on the answer.  But what does it mean? What is carat weight?  And why is carat weight important?

Diamond weight is stated in metric measurements called carats. One carat is equal to 200 milligrams, which is 1/5 of a gram or 0.20 gram. There are 142 carats in an ounce.  The carat is actually the standard unit of weight for most gemstones, helping standardise the way most gemstones are valued.

What is the history of diamond carat weights?

So, now we know the technical bits, but how did they come up with this particular way of measuring the weight of a gemstone?  Fascinatingly, the modern carat system has its roots in the carob seed, which comes from the locust tree. Because the seeds, which come from a large pod, like a bean pod,  are pretty much uniform in size and weight, they were a useful standard for determining the weight of a gem  in the very earliest times of gem trading. Early diamond merchants and jewellers used carob seeds as counterweights in hand-held balance scales.  We love this!  It’s not likely our customers would approve of diamonds from us being sold by carob weight however, so it’s unlikely we’re going to argue for a return to retro diamond weighing.

In the early 20th century carat weight was standardised as 0.20 gram. This gave buyers, sellers and owners a fixed and internationally accepted weight standard for diamonds, against which, of course, a monetary value could be set.

Carat is abbreviated as “ct” and weights are typically given to two decimal places: 1.00 ct, 0.76 ct, 1.57 ct.

Like the pound sterling, a carat is made up of 100 parts, called “points” and abbreviated as “pt.” An easy way to remember this is to think of carats as pounds and points as pennies.  Every diamond, before it is allowed to enter the public marketplace, must be given a carat weight, which forms part of its rating, along with the other Cs – colour, cut and clarity.  The carat weight of every gemstone is recorded to two decimal places – so 0.87ct, or 3.24ct, or 1.49ct, for example.

White emerald cut diamond bespoke engagement ringWhy is carat weight important?

The price of a diamond increases as its carat weight increases.  Since diamonds of 1.00 ct or larger are rarer, prices jump dramatically for these stones.  But, not all diamonds have the same value per carat as other diamonds – the value per carat (or carat point) is set according to the combination of the 4 Cs – cut, clarity and colour, as well as carat.

Carat weight also helps you compare prices between diamonds with different weights but the same colour, clarity and cut grades, allowing you to compare the per carat price for each stone to see where you’re getting the best value.  A 0.50ct stone for example, because of the nice round number, and being able to say ‘it’s a half carat’ can cost more than one that is 0.49ct a difference invisible to the naked eye ((as long as the cut, clarity and colour is the same) Strange, but true!

It also allows you to assess two stones the same carat weight, but with perhaps differing clarity or colour, and decide whether size is everything, or overall quality is preferable.  A one carat stone of a reduced clarity or slightly darker colour will cost less than a one carat stone with excellent colour and clarity, but still be big and sparkly and again, very difficult to tell the difference if you’re not a trained goldsmith or valuer.

Green tourmaline and diamond dress ringA very personal choice

All of this makes diamond selection a fascinatingly personal choice, which is why we spend as much time as we need helping our customers choose the stones they want in the jewellery they ask us to make for them. Simply by changing a single stone, while maintaining carat weight, changes to the budget can be made.

This means that by going bespoke, your dream ring is not as far out of your reach as you might think!  Hurrah!

If you want to learn more, call in or make an appointment – we love, love, love to talk diamonds!  And sapphires. And rubies. And citrines. And tourmalines. And peridot. And…well, you get the picture!

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