Diamond Carat Weight - The 4Cs of Diamonds

Carat is a word that’s often associated with gold, but it’s also how diamond weight is described. In the diamond world, one metric carat equals 200 milligrams, and then each carat is subdivided to allow highly precise measurements to the 100th decimal place.

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Diamonds are also measured for size using millimetres, so when you’re buying a diamond in an engagement ring or pendant, you need to consider both weight and size (along with the rest of the 4Cs – cut, colour and clarity).

The difference between two diamonds that have identical carat weight can be significant, because one of the diamonds might have a cut that makes it look larger or smaller. This is why at Diamonds on Richmond we only use Excellent or Very Good cut grade diamonds, this ensures that you get the best millimetre size for the carat weight without compromising on sparkle. Certain cuts – like emerald, oval and pear – often look larger than a round brilliant cut, even when the diamond carat weight is identical. Visit the GIA site for more about diamond carat weight.

What are the sizes of diamonds?

When you’re interested in a diamond, you might want to ask about the millimetre size of the stone to get a better feel for what the carat weight looks like. To generalise, a 0.50 ct round brilliant diamond will be about 5mm in diameter, while a three carat diamond will be more than 9mm.

In the diamond world, which has its own jargon, you’ll often hear the word ‘pointer’ used when describing very small diamonds. For example, a one-pointer means a 0.01 carat diamond, a two-pointer is a 0.02 carat stone, and so on.

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What's a good diamond carat size?

If you’re in the market for an engagement ring, there’s no right or wrong carat size. It will come down to personal preference and the amount you would like to spend. Generally speaking, our engagement rings start from 0.3ct and upwards, sky’s the limit! If you’re planning to propose, investing in an exceptional stone is a great start. However, diamond size isn’t everything. Cut, colour and clarity are other factors that will affect the price and determine how beautiful and captivating the diamond is. More about the 4Cs of diamonds.

What size is a 1 carat diamond?

Remembering that carat refers to weight, a one carat diamond doesn’t have a defined size. But as a ballpark, it will be around 6.5mm across. Some diamonds are deeper than others, so their widest point is narrower. Diamonds that are too deep are not ideal, because their carat weight is hidden in the depth of the stone.

It’s easy enough to find an estimated diamond size chart online, but remember that it can never be entirely accurate..

How much is a 1-carat diamond?

Diamonds vary in price considerably depending on their quality, but generally in New Zealand, a diamond ring featuring a one carat stone could cost anywhere between $5,000 and $40,000. The difference in price is because all one-carat diamonds are not created equal. Which is why it is important to understand the cut, clarity, and colour of the stone you are looking at. You also have the option of a mined diamond or a man-made diamond. Man-made diamonds cost less than mined diamonds.

What is the biggest diamond ever found?

A 3,106-carat diamond was discovered at the Premier Mine in South Africa in 1905. Weighing over 600grams and christened the ‘Cullinan’, it’s still the largest diamond ever found.

Want to know more about diamonds?

This Diamond Carat article is part of: The Diamond Buying Guide - The 4Cs of Diamonds. Learn more about the important aspects to consider when purchasing a diamond.

Then, to take it one step further, let one of our Client Managers take you through the exciting process of choosing the perfect diamond for your engagement ring.

Get in touch with us and book an appointment to kick things off.


At DOR we've made buying an engagement ring stress-free. Simply choose from our Collection, start with a proposal ring or customise one of our classic designs.


We've made it easy! Browse our designs, then tailor to your price point.


The choice is yours! At DOR we offer both lab-grown and mined diamonds.


Want a surprise proposal but don't know what design to choose?


Feeling creative? Tailor any ring in our Collection to suit your individual style



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