How big is a 1ct diamond?

Want to know how much you will get for your money when you buy a 1 carat diamond? Find out more here!

As a carat is a unit of weight used specifically for diamonds and other gemstones, then size of a 1 carat diamond can vary from 6.20 to 6.80mm diameter. The variation is due to the depth as a deep cut diamond is smaller in diameter and a shallow cut is wider. When diamonds are cut with a shallow cut they tend to look bigger but it must be remembered that if a diamond is cut wrongly i.e. too deep or too shallow, the cut quality will be poor and the diamond will lose brilliance which is crucial when it comes to quality and value.

Why use the word 'carat'?

Before we look into the intricacies of the sizes of 1ct diamonds, we should clarify exactly what a carat is; a carat is the way that all gemstones and diamonds are measured and is equal to approx. 200 milligrams so 1 gram is about 5 carats. The word 'carat' refers to the carob bean which has a fairly uniform weight and this was used to balance the scales when weighing gemstones in the past. In 1907 the carat was standardised and became a measurement of 200 mg.

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How do you weigh a diamond?

Whether your diamond is 1 carat or more, it has to be weighed very carefully on a finely calibrated electronic scale. Weight is measured in 1000th’s of a carat and then rounded up or down to the nearest 100th.
i.e.
A diamond weighing in at 1.708 carats would round down to 1.70.
A diamond weighing 1.709 would round up to 1.71.

Diamonds have been found that have been very large but also very rare with the Cullinan diamond in its rough uncut form coming in at 3107.75 carats.

How value is calculated?

As far as carats are concerned, the larger the diamond the more valuable it is but the way that the diamond is cut also reflects upon the value. With diamonds being priced per carat, quality also has to be taken into account; if you took a variety of diamonds and then compared the costs you would find a range of variations. You can work this out by dividing the selling price by the weight: a diamond weighing 1.71 carats that costs £5000 would be priced at £2924 per carat whereas a diamond of the same weight costing less, £3500, would have a price per carat of £2046.

This is due to certain factors; large diamonds are rarer so the price will be more and the carat weight will increase at the same time. This means that a 2 carat diamond will cost a lot more than twice the price of a 1 carat gemstone. In the same way, if you buy a ring made up of many small diamonds totalling 1 carat overall, it will cost less than buying a ring with a single 1 carat diamond stone.

So as you can see, a 1 carat diamond does not only vary in size but also in price. All of this adds to the beauty of diamonds and makes each one totally unique.