If you have ever wondered why a 2 carat stone does not look twice the size of a 1 carat, you are not alone. Here is what carat really means, how moissanite is measured, and how to choose the right size for her.
The quick answer
Carat measures a stone's weight, not its size. Moissanite is sold by diamond equivalent size, so a 1 carat moissanite is about 6.5 mm across, the same as a 1 carat diamond. The carat sizes we quote at HerMoment are diamond equivalent sizes, and we list the millimetre size on every piece.
What does carat mean?
Carat is a unit of weight used for gemstones. It tells you how heavy a stone is, not how big it looks.
One metric carat is 200 milligrams (0.2 g), and each carat is split into 100 points, so a "50 point" stone is half a carat (GIA). The name comes from carob seeds, which early gem traders used to balance their scales.
Think of it like buying fruit by the kilo: the weight tells you how much you have, but not exactly how big each piece looks. With jewellery, the width in millimetres is what you actually see.
Is a 1 carat moissanite the same size as a 1 carat diamond?
Yes, when it is sold by diamond equivalent weight (DEW). Here is why that label exists.
Moissanite is a slightly lighter material than diamond. GIA measures moissanite at a specific gravity of 3.22 (GIA Gems & Gemology) and diamond at 3.52 (GIA), which means moissanite weighs about 9% less than a diamond of the same size. So if you put a 6.5 mm moissanite and a 6.5 mm diamond on a scale, the diamond weighs 1 carat and the moissanite about 0.9 carat, even though they look exactly the same.
If moissanite were labelled by its true weight, a stone that looks just like a 1 carat diamond would be called "0.9 carat" and sound smaller than it is. So jewellers use DEW, which answers one simple question: how big would this look if it were a diamond?
At HerMoment, every carat size we quote is a diamond equivalent size. When you see "1 carat" on our site, you are getting a stone the same size as a 1 carat diamond, about 6.5 mm across.
Moissanite carat size chart
Here is how each size compares, from dainty to bold.
Round stones shown to scale with each other, not actual size.
| Size (DEW) | Round | Heart | Oval | About the size of | Lovely for |
|---|---|---|---|---|---|
| 0.5 ct | 5 mm | 5 mm | 6 x 4 mm | a peppercorn | dainty pieces, layering, studs |
| 1 ct | 6.5 mm | 6.5 mm | 7.5 x 5.5 mm | the width of a pencil | a classic everyday pendant or ring |
| 1.5 ct | 7.5 mm | 7.5 mm | 8.5 x 6.5 mm | the end of a pencil eraser | everyday wear with more presence |
| 2 ct | 8 mm | 8 mm | 9 x 7 mm | a garden pea | a statement gift |
| 3 ct | 9.3 mm | 9 mm | 10 x 8 mm | a small blueberry | evenings out, bold looks |
Sizes are approximate. Oval sizes are length x width. Shape changes the look too: an oval tends to look larger than a round of the same carat, because its sparkle spreads along a longer outline.
Does a 2 carat moissanite look twice as big as a 1 carat?
No, and this surprises most people.
A stone is three dimensional. When you look at a necklace or ring, you only see the top of the stone, but it also has depth underneath. When the weight doubles, a lot of that extra weight goes into depth you can't see. As GIA puts it, "you won't see this weight when the diamond is mounted" (GIA).
So a 2 carat round is about 8 mm across, compared with 6.5 mm for a 1 carat. That is double the weight, but only about 23% wider, with around 50% more sparkle showing from the top. It still looks clearly bigger, just not twice the size.
What carat size should I choose?
The right size is the one she will actually wear, so start with her style rather than the biggest number.
- If her jewellery is fine and simple: 0.5 to 1 carat will feel natural.
- For an everyday necklace or ring: 1 carat (6.5 mm) is the classic choice, easy to wear to work and on weekends.
- For a statement gift: 2 carat (8 mm) is noticed from across the room.
- For stud earrings: 0.5 to 1 carat each. Check the wording: "1 carat total" means two 0.5 carat studs.
- If you are not sure: 1 carat in a round or heart suits almost every style.
One last tip: when comparing brands, compare the millimetre size, not just the carat. Two "2 carat" pieces can differ in size if one brand quotes true weight and the other quotes diamond equivalent size.
Sources: GIA 4Cs: Diamond carat weight · GIA 4Cs: Understanding carat weight · GIA: Diamond facts · GIA Gems & Gemology: Synthetic Moissanite (1997)
