Guide · 4 min read · Updated 2026-08-28
Almost everyone orders by carat, while what they are picturing is how wide the stone will be. Those are not the same number, and the gap is wide enough to disappoint.
Carat measures weight, not width
Carat is a unit of weight, and moissanite is slightly lighter than diamond at the same physical size. A moissanite as wide as a one-carat diamond therefore weighs a little under a carat.
That is why moissanite is usually sold by diamond-equivalent size: the number you see describes how wide the stone is, not what it weighs. Millimetres are what decides how it looks.
Millimetre guide for round stones
Rough figures, enough to picture it:
- 0.5CT — about 5 mm
- 1CT — about 6.5 mm
- 2CT — about 8 mm
- 3CT — about 9.3 mm
- 5CT — about 11 mm
A slimmer finger makes a stone look larger
The same stone reads much larger on a US 4 finger than on a US 9, because the eye measures it against the finger around it.
Below a US 6, one carat often already feels full. Above a US 8, the same stone can read small, and two carats becomes the more sensible place to start.
It cuts both ways: a large stone on a slim finger looks striking, but the setting sits higher and catches on things more often.
Where extra carats stop showing
The step from 0.5CT to 1CT is obvious — about a third wider. The step from 3CT to 4CT is much harder to see, and costs a great deal more.
On a fixed budget, the money usually shows more going from 1CT to 2CT than from 3CT to 4CT.
If you are still unsure
Cut a paper circle to the millimetre sizes above and wear it taped to your finger for a day. It sounds crude, and it is far more honest than judging from a photograph — product shots are taken close up, and scale on a screen always lies.
You are also welcome to send us a photo of your hand on WhatsApp. We will tell you honestly which size we think suits it.