Diamond Size Chart

Want to know the actual size of a 1 carat diamond on a hand? Use this diamond size chart to convert millimeters (mm) to carat weight for every popular shape. It works for both lab grown and mined diamonds, because they have the same density.

Quick Answers: Diamond Size in mm

1 carat round diamond: about 6.5 mm across.
2 carat round diamond: about 8.0 mm across.
How big is a 4 mm diamond? About 0.25 carat, a quarter carat.
Small melee stones: 1.3 mm is about 0.01 ct, 1.8 mm about 0.025 ct, 2 mm about 0.03 ct.

Moissanite Size to Carat

Moissanite is about 10% lighter than diamond, so it is sold by millimeter size and a diamond equivalent weight. A 6.5 mm round moissanite looks like a 1 carat diamond but actually weighs about 0.88 to 0.9 carat. Use the mm sizes in the chart below for both stones. Not sure which to choose? Read our moissanite vs lab grown diamond guide.

Select your shape below. Ready to shop? Browse lab diamond solitaire rings or moissanite solitaire rings, and check your fit with our ring size chart.

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Diamond Size Chart

Compare the actual size and carat weight of different diamond shapes.

Select your diamond shape:

Round Diamond Size Chart

Approximate millimeter measurements for each carat weight.

MM Size	Carat Weight
4 mm	0.25 ct
5.0 mm	0.50 ct
5.75 mm	0.75 ct
6.5 mm	1.00 ct
6.8 mm	1.25 ct
7.3 mm	1.50 ct
7.75 mm	1.75 ct
8 mm	2.00 ct
8.7 mm	2.50 ct
9.1 mm	3.00 ct
9.75 mm	3.50 ct
10.25 mm	4.00 ct
10.75 mm	4.50 ct
11 mm	5.00 ct

Princess Diamond Size Chart

Approximate millimeter measurements for each carat weight.

MM Size	Carat Weight
3.25 mm.	0.25 ct.
4.5 mm.	0.50 ct.
5 mm.	0.75 ct.
5.5 mm.	1.00 ct.
6 mm.	1.25 ct.
6.5 mm.	1.50 ct.
6.75 mm.	1.75 ct.
7 mm.	2.00 ct.
7.5 mm.	2.50 ct.
8 mm.	3.00 ct.
8.5 mm.	3.50 ct.
8.75 mm.	4.00 ct.
9.25 mm.	4.50 ct.
9.5 mm.	5.00 ct.

Cushion Diamond Size Chart

Approximate millimeter measurements for each carat weight.

MM Size	Carat Weight
3.25 mm.	0.25 ct.
4.9 mm.	0.50 ct.
5.25 mm.	0.75 ct.
5.5 mm.	1.00 ct.
6 mm.	1.25 ct.
6.5 mm.	1.50 ct.
6.75 mm.	1.75 ct.
7 mm.	2.00 ct.
7.5 mm.	2.50 ct.
8 mm.	3.00 ct.
8.5 mm.	3.50 ct.
9 mm.	4.00 ct.
9.3 mm.	4.50 ct.
9.5 mm.	5.00 ct.

Emerald Diamond Size Chart

Approximate millimeter measurements for each carat weight.

MM Size	Carat Weight
4.30x3 mm.	0.25 ct.
6x4 mm.	0.50 ct.
6.5x4.5 mm.	0.75 ct.
7x5 mm.	1.00 ct.
7.5x5.3 mm.	1.25 ct.
7.5x5.5 mm.	1.50 ct.
8x6 mm.	1.75 ct.
8.5x6.5 mm.	2.00 ct.
9x7 mm.	2.50 ct.
9.3x7.5 mm.	3.00 ct.
9.75x7 mm.	3.50 ct.
10x8 mm.	4.00 ct.
10.5x8.5 mm.	4.50 ct.
11x9 mm.	5.00 ct.

Heart Diamond Size Chart

Approximate millimeter measurements for each carat weight.

MM Size	Carat Weight
4 mm.	0.25 ct.
5 mm.	0.50 ct.
6 mm.	0.75 ct.
6.5 mm.	1.00 ct.
7 mm.	1.25 ct.
7.5 mm.	1.50 ct.
7.7 mm.	1.75 ct.
8 mm.	2.00 ct.
8.5 mm.	2.50 ct.
9 mm.	3.00 ct.
10 mm.	3.50 ct.
10.5 mm.	4.00 ct.
11 mm.	4.50 ct.
11.5 mm.	5.00 ct.

Marquise Diamond Size Chart

Approximate millimeter measurements for each carat weight.

MM Size	Carat Weight
6x3 mm.	0.25 ct.
8x4 mm.	0.50 ct.
9x4.5 mm.	0.75 ct.
10x5 mm.	1.00 ct.
11x5.5 mm.	1.25 ct.
12x6 mm.	1.50 ct.
12.5x6.25 mm.	1.75 ct.
13x6.5 mm.	2.00 ct.
14x7 mm.	2.50 ct.
15x7 mm.	3.00 ct.
15x8 mm.	3.50 ct.
16.5x8.25 mm.	4.00 ct.
16.75x8.5 mm.	4.50 ct.
17x8.5 mm.	5.00 ct.

Emerald Diamond Size Chart

Approximate millimeter measurements for each carat weight.

MM Size	Carat Weight
4.3x3 mm.	0.25 ct.
6x4 mm.	0.50 ct.
6.5x4.5 mm.	0.75 ct.
7x5 mm.	1.00 ct.
7.5x5.3 mm.	1.25 ct.
7.5x5.5 mm.	1.50 ct.
8x6 mm.	1.75 ct.
8.5x6.5 mm.	2.00 ct.
9x7 mm.	2.50 ct.
9.3x7.5 mm.	3.00 ct.
9.75x7 mm.	3.50 ct.
10x8 mm.	4.00 ct.
10.5x8.5 mm.	4.50 ct.
11x9 mm.	5.00 ct.

Oval Diamond Size Chart

Approximate millimeter measurements for each carat weight.

MM Size	Carat Weight
5x3 mm.	0.25 ct.
6x4 mm.	0.50 ct.
7x5 mm.	0.75 ct.
7.7x5.7 mm.	1.00 ct.
8x6 mm.	1.25 ct.
8.5x6.5 mm.	1.50 ct.
9x6.5 mm.	1.75 ct.
9x7 mm.	2.00 ct.
10x8 mm.	2.50 ct.
12x8 mm.	3.00 ct.
12x8.5 mm.	3.50 ct.
12.5x8.5 mm.	4.00 ct.
12.75x8.5 mm.	4.50 ct.
12x10 mm.	5.00 ct.

Pear Diamond Size Chart

Approximate millimeter measurements for each carat weight.

MM Size	Carat Weight
5x3 mm.	0.25 ct.
6x4 mm.	0.50 ct.
7x5 mm.	0.75 ct.
7.7x5.7 mm.	1.00 ct.
8x6 mm.	1.25 ct.
8.5x6.5 mm.	1.50 ct.
10x6 mm.	1.75 ct.
9x7 mm.	2.00 ct.
10x8 mm.	2.50 ct.
12x8 mm.	3.00 ct.
12x9 mm.	3.50 ct.
14x8 mm.	4.00 ct.
14.5x9 mm.	4.50 ct.
15x9 mm.	5.00 ct.

Radiant Diamond Size Chart

Approximate millimeter measurements for each carat weight.

MM Size	Carat Weight
4.3x3 mm.	0.25 ct.
6x4 mm.	0.50 ct.
6.5x4.5 mm.	0.75 ct.
7x5 mm.	1.00 ct.
7.3x5.5 mm.	1.25 ct.
7.5x5.8 mm.	1.50 ct.
8x6 mm.	1.75 ct.
8.2x6.2 mm.	2.00 ct.
9x7 mm.	2.50 ct.
9.5x7.5 mm.	3.00 ct.
10x8 mm.	3.50 ct.
10.2x8.2 mm.	4.00 ct.
10.5x8.5 mm.	4.50 ct.
11x9 mm.	5.00 ct.

Asscher Diamond Size Chart

Approximate millimeter measurements for each carat weight.

MM Size	Carat Weight
3.25 mm.	0.25 ct.
4.5 mm.	0.50 ct.
5 mm.	0.75 ct.
5.5 mm.	1.00 ct.
6 mm.	1.25 ct.
6.5 mm.	1.50 ct.
6.7 mm.	1.75 ct.
7 mm.	2.00 ct.
7.5 mm.	2.50 ct.
8 mm.	3.00 ct.
8.5 mm.	3.50 ct.
9 mm.	4.00 ct.
9.25 mm.	4.50 ct.
9.5 mm.	5.00 ct.

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