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Diamond Size Guide

The same carat weight can look different. Compare dimensions and find the proportions you prefer.

03 Understanding diamond size

01 Carats measure weight; millimetres measure size

1 ct = 0.2 g; 1 point = 0.01 ct. Use millimetres to compare visible size.

02 Compare two diamonds at the same scale

Save one diamond, then adjust the other to compare.

03 Have measurements? Enter them directly

Use the measured height and width for your comparison.

Common questions

Why can diamonds of the same carat weight differ in size?

Carats measure weight. Shape, proportions and depth affect how large a diamond looks from above.

How do I read the measurements on a grading report?

Fancy shapes are usually listed as length × width × depth. Enter the first two measurements. For a round diamond, average the minimum and maximum diameters and enter that value in both fields.

Are melee weights per diamond or combined?

The chart lists individual weights. Ten diamonds of 0.01 ct total 0.10 ct, but each is smaller than a single 0.10 ct diamond.

Can I compare natural and lab-grown diamonds?

Yes. Both use carats for weight and millimetres for dimensions, so the same comparison applies.

How do I calibrate my screen?

Choose “Calibrate screen”, adjust the line to match 50 mm on a physical ruler, then apply. Recalibrate after changing screens or page zoom.

Size and proportions

Chart dimensions are a guide. Diamonds of the same carat weight can have different dimensions.

Compare round diamonds by diameter and fancy shapes by height × width. A higher ratio gives a more elongated outline.

Round size reference chart

ctmm
0.00250.8 × 0.8
0.0051 × 1
0.0091.2 × 1.2
0.011.3 × 1.3
0.0151.5 × 1.5
0.021.75 × 1.75
0.0251.8 × 1.8
0.032 × 2
0.042.2 × 2.2
0.062.5 × 2.5
0.082.75 × 2.75
0.13 × 3
0.143.25 × 3.25
0.173.5 × 3.5
0.213.75 × 3.75
0.254 × 4
0.284.25 × 4.25
0.364.5 × 4.5
0.444.75 × 4.75
0.55 × 5
0.665.5 × 5.5
0.755.75 × 5.75
0.846 × 6
0.936.25 × 6.25
16.5 × 6.5
1.256.8 × 6.8
1.57.3 × 7.3
1.757.75 × 7.75
28 × 8
2.58.7 × 8.7
39.1 × 9.1
3.59.75 × 9.75
410.25 × 10.25
4.510.75 × 10.75
511 × 11
6.8412 × 12
8.5113 × 13
10.4914 × 14
12.8915 × 15
16.0616 × 16

Oval size reference chart

ctmm
0.13.6 × 2.7
0.154 × 3
0.24.8 × 3
0.255 × 3
0.335.5 × 3.5
0.355.5 × 3.7
0.56 × 4
0.757 × 5
17.7 × 5.7
1.258 × 6
1.58.5 × 6.5
1.759 × 6.5
29 × 7
2.510 × 8
312 × 8
3.512 × 8.5
412.5 × 8.5
4.512.75 × 8.5
513 × 9
6.0514 × 10.4
8.2114 × 12
9.3216 × 12
11.8816 × 14
12.8618 × 13
14.9620 × 15

Heart size reference chart

ctmm
0.183.5 × 3.5
0.254 × 4
0.284.25 × 4.25
0.344.5 × 4.5
0.384.75 × 4.75
0.55 × 5
0.615.5 × 5.5
0.756 × 6
16.5 × 6.5
1.257 × 7
1.57.5 × 7.5
1.757.7 × 7.7
28 × 8
2.58.5 × 8.5
39 × 9
3.510 × 10
410.5 × 10.5
4.511 × 11
511.5 × 11.5
5.6612 × 12
7.8813 × 13
9.3814 × 14
10.7915 × 15
13.2716 × 16
15.3318 × 18

Princess size reference chart

ctmm
0.0151.5 × 1.5
0.031.75 × 1.75
0.062 × 2
0.082.25 × 2.25
0.12.5 × 2.5
0.132.75 × 2.75
0.183 × 3
0.253.25 × 3.25
0.293.5 × 3.5
0.394 × 4
0.54.5 × 4.5
0.755 × 5
15.5 × 5.5
1.256 × 6
1.56.5 × 6.5
1.756.75 × 6.75
27 × 7
2.57.5 × 7.5
38 × 8
3.58.5 × 8.5
48.75 × 8.75
4.59.25 × 9.25
59.5 × 9.5
5.6210 × 10
7.4411 × 11
9.5212 × 12

Pear size reference chart

ctmm
0.133 × 2
0.184 × 2.5
0.214 × 3
0.255 × 3
0.355 × 4
0.56 × 4
0.757 × 5
17.7 × 5.7
1.258 × 6
1.58.5 × 6.5
1.7510 × 6
29 × 7
2.510 × 8
312 × 8
3.512 × 9
414 × 8
4.514.5 × 9
515 × 9
6.2716 × 10
7.3617 × 11
8.1418 × 11
9.3518 × 12
10.2118 × 13

Cushion size reference chart

ctmm
0.253.25 × 3.25
0.44.2 × 4.2
0.54.9 × 4.9
0.755.25 × 5.25
15.5 × 5.5
1.256 × 6
1.56.5 × 6.5
1.756.75 × 6.75
27 × 7
2.57.5 × 7.5
38 × 8
3.58.5 × 8.5
49 × 9
4.59.3 × 9.3
59.5 × 9.5
5.6210 × 10
7.4411 × 11
9.5212 × 12
12.6613 × 13

Emerald size reference chart

ctmm
0.13 × 2
0.123.5 × 2
0.154 × 2
0.24 × 3
0.254.3 × 3
0.295 × 3
0.465.5 × 3.5
0.56 × 4
0.756.5 × 4.5
17 × 5
1.257.3 × 5.3
1.57.5 × 5.5
1.758 × 6
28.5 × 6.5
2.59 × 7
39.3 × 7.5
3.59.75 × 7.7
410 × 8
4.510.5 × 8.5
511 × 9
612 × 10
8.4814 × 10
9.1313 × 11
11.2614 × 12
14.2216 × 12

Radiant size reference chart

ctmm
0.254.3 × 3
0.344.8 × 3.2
0.415.5 × 3.3
0.56 × 4
0.756.5 × 4.5
17 × 5
1.257.3 × 5.5
1.57.5 × 5.8
1.758 × 6
28.2 × 6.2
2.258.5 × 6.5
2.59 × 7
39.5 × 7.5
3.510 × 8
410.2 × 8.2
4.510.5 × 8.5
511 × 9
6.0612 × 9
8.4714 × 10
10.1914.4 × 10.6
12.1415 × 12
14.2216 × 12

Marquise size reference chart

ctmm
0.0253 × 1.5
0.0653.5 × 1.75
0.073.5 × 2
0.13.7 × 2
0.124.25 × 2.25
0.145 × 2.5
0.165.5 × 2.75
0.185.5 × 3
0.26 × 3
0.256.7 × 3
0.37 × 3
0.58 × 4
0.759 × 4.5
110 × 5
1.2511 × 5.5
1.512 × 6
1.7512.5 × 6.25
213 × 6.5
2.514 × 7
315 × 7
3.515 × 8
416.5 × 8.25
4.516.75 × 8.5
517 × 8.5
5.517.5 × 10
7.9420 × 10
9.520 × 11

Asscher size reference chart

ctmm
0.253.25 × 3.25
0.394 × 4
0.54.5 × 4.5
0.755 × 5
15.5 × 5.5
1.256 × 6
1.56.5 × 6.5
1.756.7 × 6.7
27 × 7
2.57.5 × 7.5
38 × 8
3.58.5 × 8.5
49 × 9
4.59.25 × 9.25
59.5 × 9.5
5.6210 × 10
7.4411 × 11
9.5212 × 12
12.6613 × 13
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