Moissanite Size Chart: Millimetres to Carat, and How Big It Looks

Moissanite is sold by millimetre size, but everyone talks in carats. Here is how the two line up for round brilliant stones.

Round brilliant conversion

• 5.0mm ≈ 0.5ct equivalent
• 6.5mm ≈ 1.0ct equivalent
• 7.5mm ≈ 1.5ct equivalent
• 8.0mm ≈ 2.0ct equivalent
• 9.0mm ≈ 2.75ct equivalent

Moissanite is lighter than diamond, so a 6.5mm moissanite actually weighs less than a 1ct diamond while looking the same size — which is why 'carat equivalent' is the honest way to describe it.

How big it looks on the finger

Finger size changes perceived size significantly. A 6.5mm stone reads larger on a size 4 finger than on a size 8. As a rule, 6.5mm looks generous on small hands and modest on larger ones.

Fancy shapes and face-up size

Oval, emerald, pear and marquise give more face-up area per carat than round. An 8x6mm oval (≈1.5ct) can appear larger than a 7.5mm round of similar weight.

How to choose

• Delicate stacking look: 5.0mm (0.5ct)
• Classic engagement ring: 6.5mm (1.0ct)
• Statement stone: 8.0mm (2.0ct) and above

Compare sizes with real stones in loose stones.