Quick answer
A moissanite carat size chart converts millimeters into DEW (diamond equivalent weight): the weight a diamond of the same size would have. For round stones, 5mm is 0.5 ct, 6.5mm is 1 ct, 8mm is 2 ct, 9mm is 3 ct and 11mm is 5 ct. Moissanite is about 10% lighter than diamond, so always shop by millimeters.
Carats confuse almost everyone, and moissanite adds a twist: the carat number on the label is not what the stone actually weighs. The millimeters, on the other hand, never lie.
This guide gives you the full round chart, the common sizes for ovals, emerald cuts and pears, and what each size really looks like on a finger and an earlobe.
Key takeaways
- Moissanite is sold by DEW, the weight of a diamond of the same size.
- The anchor sizes: 6.5mm = 1 ct, 8mm = 2 ct, 9mm = 3 ct.
- Carat weight grows with volume, so 1.5mm more width nearly doubles the carats.
- Oval, pear and marquise shapes look larger than a round of the same carat weight.
What does DEW mean on a moissanite?
A carat is a unit of weight: 200 milligrams, split into 100 points. As GIA puts it, carat measures weight, not size. Diamond buyers learned to picture a size from the weight, because diamonds of a given shape and cut weigh about the same for their size.
Moissanite breaks that shortcut. Its density is about 3.21 g/cm3, against 3.52 for diamond, so a moissanite weighs roughly 10% less than a diamond of identical size. A 6.5mm round moissanite looks exactly like a 1 carat diamond but weighs about 0.88 ct.
To keep things comparable, sellers label moissanite by diamond equivalent weight. “1 ct DEW” means “the size of a 1 carat diamond”. Every carat figure on Daellia product pages is DEW. Learn more about the stone itself in our moissanite guide.
Good to know
Some stud listings give the carat weight per stud, others the total for the pair (ctw). Daellia lists per stud, so a pair of 1 ct studs is 2 ctw. Check which one a listing means before you compare.
Moissanite carat size chart for round stones
These are the round sizes you will meet most often, with the DEW each one is sold as. Round is the most common cut, and the one diamond charts are built on.
| Diameter | DEW per stone | Pair of studs | How it reads |
|---|---|---|---|
| 3mm | 0.1 ct | 0.2 ctw | A pinpoint of light, ideal for second piercings |
| 4mm | 0.25 to 0.3 ct | 0.5 to 0.6 ctw | Small and discreet |
| 5mm | 0.5 ct | 1 ctw | The everyday sweet spot |
| 6mm | 0.75 to 0.8 ct | 1.5 to 1.6 ctw | Clearly visible, still quiet |
| 6.5mm | 1 ct | 2 ctw | The classic 1 carat look |
| 7mm | 1.25 ct | 2.5 ctw | A step up you can see |
| 7.5mm | 1.5 ct | 3 ctw | Noticed across a table |
| 8mm | 2 ct | 4 ctw | A statement |
| 8.5mm | 2.5 ct | 5 ctw | Bold on slim fingers |
| 9mm | 3 ct | 6 ctw | Unmistakably large |
| 10mm | 4 ct | 8 ctw | Evening and red-carpet size |
| 11mm | 5 ct | 10 ctw | Maximal, and meant to be |
DEW for round brilliant moissanite. Diamond charts from different sellers can differ by 0.2 to 0.3mm at the same weight.
Look at the jump from 6.5mm to 8mm. The stone gets only 1.5mm wider, yet the carat weight doubles. Weight follows volume, which grows with the cube of the width, so each extra millimeter adds more carats than the one before.
That is good news for your budget: going from 1 ct to 2 ct looks like a clear upgrade, not twice the stone. It is also why a 9mm stud (3 ct) can feel far bigger than a 6.5mm (1 ct) when the difference is only 2.5mm.
How big is a 1 carat moissanite?
A 1 carat round moissanite measures 6.5mm across. For scale, a US dime is 17.91mm wide, so a 1 ct stone spans a little more than a third of a dime. On the finger, it reads as a clear, classic solitaire without looking oversized.
As a stud, 6.5mm is the classic 1 carat size. It shows well with hair up or down, and it still looks right with a T-shirt. If you want something softer for daily wear, 5mm (0.5 ct) is the size to try.
How big is a 2 carat or 3 carat moissanite?
A 2 carat round is 8mm across; a 3 carat round is 9mm, almost exactly half the width of a dime. The best way to judge them is against your own finger. The table compares each stone's width with the inside diameter of common US ring sizes.
| Round stone | Size 6 (16.5mm) | Size 7 (17.3mm) | Size 8 (18.1mm) |
|---|---|---|---|
| 5mm (0.5 ct) | 30% | 29% | 28% |
| 6.5mm (1 ct) | 39% | 38% | 36% |
| 8mm (2 ct) | 48% | 46% | 44% |
| 9mm (3 ct) | 55% | 52% | 50% |
| 11mm (5 ct) | 67% | 64% | 61% |
Stone width as a share of the ring's inside diameter. The same stone looks bigger on a smaller finger.
A simple rule: once a stone covers about half the width of your finger, it reads as a statement. On a size 6, that happens around 8mm to 9mm. Not sure of your size? Our ring size guide shows you how to measure at home.
Oval, emerald and pear sizes: mm to carat
Long shapes spread their weight over a bigger face. On Brilliant Earth's diamond chart, a 1 ct oval measures about 8×5.5mm and a 1 ct round about 6.3mm. Do the math and the oval shows roughly 10% more surface for the same weight. That is why ovals, pears and marquises look generous.
| Shape | Daellia sizes (DEW) | Diamond chart reference |
|---|---|---|
| Oval | 6×4mm (0.5 ct), 9×7mm (2 ct), 11×8mm (4 ct) | 1 ct about 8×5.5mm; 2 ct about 10×7mm |
| Emerald | 5×3mm (0.5 ct) to 8×6mm (2 ct) studs; 9×7mm ring | 1 ct about 7×4.5mm; 2.5 ct about 9×6.5mm |
| Pear | 6×4mm (0.5 ct) to 12×8mm (3 ct) | 1 ct about 9×5.5mm; 3 ct about 13×8mm |
| Princess | 4×4mm (0.4 ct) to 7×7mm (2 ct) | 1 ct about 5.5mm; 2 ct about 7mm |
| Marquise | 10×5mm (1 ct), 14×7mm (3 ct) | 1 ct about 10.5×5mm; 3 ct about 15×7.5mm |
Diamond references from Brilliant Earth's mm-to-carat chart. Cutters calibrate differently, so read the millimeters.
Notice that moissanite ovals are often cut a little wider than diamond ovals. The Olympe oval ring holds a 9×7mm stone sold as 2 ct DEW, while a 2 ct diamond oval is closer to 10×7mm. The Joséphine emerald-cut ring is also 9×7mm, which sits between 2.5 and 3 ct on diamond charts.
Which moissanite size should you choose?
There is no correct size, only the one that fits how you live. These starting points work for most people:
- Second or third piercing: 3mm to 4mm studs.
- Everyday studs: 5mm to 6.5mm (0.5 to 1 ct each).
- Evening or statement studs: 8mm and up.
- Engagement ring on a slim finger (size 4 to 6): 6.5mm to 8mm already reads large.
- Engagement ring on a longer finger: 8mm to 9mm, or an oval, which flatters length.
- Solitaire necklace: 6.5mm to 8mm shows well at the collarbone.
Our tip: cut a small circle of paper at the diameter you are considering and hold it to your ear or finger in a mirror. It takes a minute and settles most debates. Compare the pieces below, then read moissanite vs lab-grown diamond if you are still weighing the stone itself.
Sizes to try
Find your stud size
Round, oval, pear and emerald cut studs, from a 3mm sparkle to a 9mm statement. D color, VVS1 moissanite.
Shop studsFrequently asked questions
Is a 6.5mm moissanite 1 carat?
Yes, in diamond equivalent weight. A 6.5mm round moissanite is the same size as a 1 carat round diamond, so it is sold as 1 ct DEW. On a scale it weighs about 0.88 ct, because moissanite is roughly 10% less dense than diamond. What you see on the finger is the same size.
Why does moissanite weigh less than a diamond of the same size?
Density. Moissanite (silicon carbide) has a density of about 3.21 g/cm3, while diamond is about 3.52 g/cm3. Two stones cut to the same shape and millimeter size therefore weigh differently, with the moissanite about 10% lighter. That is why sellers quote diamond equivalent weight instead of actual carats.
How many millimeters is a 2 carat moissanite?
A 2 carat DEW round moissanite measures about 8mm across. In an oval, Daellia's 2 ct stone measures 9×7mm. Other shapes vary with their proportions, so check the millimeter size on each listing rather than relying on the carat number alone.
What size moissanite studs look most natural?
For everyday wear, 5mm to 6.5mm per stud (0.5 to 1 ct DEW) looks natural on most earlobes. Smaller sizes like 3mm and 4mm suit second piercings. From 8mm up, studs read as a deliberate statement, which is lovely for evenings but more noticeable at the office.
Does a 1 carat moissanite look bigger than a 1 carat diamond?
Not when the carat is DEW: 1 ct DEW means the size of a 1 carat diamond, so they look the same. If a moissanite weighed a true 1.00 ct on a scale, it would be slightly larger, about 6.7mm instead of 6.5mm, because it is less dense.
Keep reading
Written by the Daellia Journal team, Paris. We write about moissanite, metals and the stories behind fine jewelry so you can buy with confidence. Read our moissanite guide or our story.
