People will often say "I want a one-carat diamond". What they don't realize is that 'carat' refers to the weightof a diamond rather than the size of the diamond, and two diamonds of the same carat weight can be completely different sizes. A one carat emerald cut diamond for example, will look noticeably bigger than a one carat princess cut. Confusing right? That's why we're sharing the charts below so you can easily convert carat to mm and find out the true size of every shape of stone.
Keep in mind, these mm to carat conversions are approximate and depend on many different factors. If one diamond is cut poorly for example, it could carry more weight on the bottom of the diamond, making it appear smaller from the top view.
If you’re ever not sure about a diamond’s size, send us a message anytime and we'll send you measurements and videos to give you a clear idea of the ring/stone on a finger.
MM to Carat Conversion For Round Diamonds + Oval Diamonds
round brilliant
By far the most favored diamond shape, round brilliant diamonds are created using precision angles and proportions for the most sparkling, blindingly brilliant diamond possible. Because of their facet pattern, you can opt for a lower clarity grade than other diamond shapes and still have an eye-clean diamond. Round brilliant diamonds will usually look smaller than other shapes with a similar carat weight.
Keep in mind, the chart below is strictly for round brilliant diamonds – other round diamonds with a different cut like rose cut diamonds, old European diamonds, antique cuts, or poorly cut diamonds will vary in size from this chart.
OVAL CUT
Oval shaped stones trail justbehind round brilliant diamonds in terms of brilliance and sparkle factor. Where they win is their size per carat: an oval cut diamond looks larger than other diamonds of a similar carat weight. They’re also super flattering - elongating the look of shorter fingers and offering more finger coverage on larger hands – the best of all worlds.
MM to Carat Conversion For Emerald Cut Diamonds + Princess Cut Diamonds
Emerald cut
The art-deco, rectangular stone you can’t help but love, emerald cut diamonds belong to a family called “Step Cuts” – this describes the parallel, graduated lines in the diamond cut. Unlike the disco ball effect of brilliant cut diamonds, step cuts give off flashes of white light as it moves through the steps. Because of the clear, unobstructed diamond top, blemishes and inclusions are seen more clearly in a step cut diamond – opt for a higher clarity grade (versus a brilliant cut diamond) if you’re looking for an eye-clean diamond .
Princess cut
Princess cut diamonds are the square cousin to round brilliant diamonds – the same brilliant sparkle with four edgy edges. Because they’re measured diagonally, princess cuts usually look larger than their carat weight suggests. The chart below only shows one mm measurement since most princess cuts are a perfect square. So, when it says 5.5 mm - that means 5.5 x 5.5 mm!
Emerald cut diamond ring in white gold - sold, reach out to commission something similar
Princess cut diamond ring. Sold, reach out to commission something similar
MM to Carat Conversion For Marquise Diamonds + Asscher Diamonds
MarquisE
Marquise diamonds look like an oval with pointed ends – a super flattering shape that slims and elongates the look of fingers. As a member of the brilliant cut family, they’re incredibly sparkly and shine bright in every light. They’re measured from point to point and at their widest point in the center of the stone.
ASSCHER CUT
Another step cut stone, asscher cut diamonds are known as the ‘square emerald cut’. Asschers have a hall-of-mirrors effect, with a sparkle that seems to go forever inside the stone. If you follow on us IG, you know the asscher from our Founder, Catherine’s engagement ring! As with all step cuts, prioritize clarity since these stones have an obstructed top view that will show blemishes more clearly than brilliant cut stones.
Asscher cut diamond ring in Peach Gold - sold, reach out to commission something similar
Marquise cut diamond ring. Sold, reach out to commission something similar
MM to Carat Conversion For Pear Cut Diamonds + Cushion Cut Diamonds
PEAR SHAPED
Also considered a brilliant cut diamond, pear shaped stones come close to round brilliant diamonds in terms of brilliance and sparkle factor. Where they win is their size per carat: an oval cut diamond looks larger than round brilliant diamonds with a similar carat weight. They’re also super flattering - elongating the look of your hand and covering more of the finger. Pears are also less expensive than round brilliant diamonds.
cushion cuts
Cushion cut stones are square or rectangular with rounded corners – just like a cushion (a name that fits). With a brilliant cutting style, these diamonds are incredibly brilliant with a scintillating sparkle. Like the emerald cut, cushions have an more open table (top), so inclusions can be seen easier – opt for a higher clarity grade for an eye-clean diamond. The chart below refers to perfectly square cushion cuts – 5.5 mm means 5.5 x 5.5 mm.
Pear cut diamond ring - sold, reach out to commission something similar
Cushion cut diamond ring - sold, reach out to commission something similar
MM to Carat Conversion For Radiant Cut Diamonds + Heart Shaped Diamonds
Radiant Cut
Radiant cut diamonds are a magical marriage between a brilliant cut and an emerald cut – scintillating sparkle + clean, geometric lines. Radiant cuts use more of the rough diamond than other stones, cutting down on waste and cost, which we love. These stones can be either square or rectangular, but the chart below shows dimensions for elongated radiant cuts.
Heart shaped
The most universally recognized symbol of love, a heart has deep meaning and sentimentality attached to it. Incredibly difficult to cut perfectly, heart shaped diamonds start out as pears and are then cut into the distinctive heart. The chart below shows measurements of a heart-shaped diamond’s widest point.
Heart shaped champagne diamond ring - sold, reach out to commision something similar