Round vs Marquise diamond size

By HeyGema™ · Updated November 5, 2026

In short

A 1 carat round measures 6.5 mm and a 1 carat marquise 10.4 x 5.2 mm. At the same weight a marquise faces up about 16% larger than a round. In face-up terms, 1 carat of round looks like a 1.00 carat round and 1 carat of marquise like a 1.25 carat round.

6.5 mm1 ct round
10.4 x 5.2 mm1 ct marquise
+16%marquise face-up vs round

Carat to mm calculator

ShapeGemCaratLength to width

About 10.4 x 5.2 mm

An estimate for a well-cut stone. A deep or shallow cut faces up smaller or bigger.

1 ct round

6.5 mm

1 ct marquise

10.4 x 5.2 mm

Side by side

1 ct round inside 1 ct marquise

A 1 carat round and a 1 carat marquise diamond, to the same scale.

Round vs Marquise diamond size at the same weight

At the same weight a marquise faces up about 16% larger than a round. A 1 carat round measures 6.5 mm and a 1 carat marquise 10.4 x 5.2 mm. A 1 carat round faces up like a 1.00 carat round, and a 1 carat marquise like a 1.25 carat round.

0.5 carat: Round length x width: 5.1 mm; Marquise length x width: 8.3 x 4.1 mm; Marquise face-up vs round: +16%

0.75 carat: Round length x width: 5.9 mm; Marquise length x width: 9.4 x 4.7 mm; Marquise face-up vs round: +16%

1 carat: Round length x width: 6.5 mm; Marquise length x width: 10.4 x 5.2 mm; Marquise face-up vs round: +16%

1.5 carat: Round length x width: 7.4 mm; Marquise length x width: 11.9 x 6.0 mm; Marquise face-up vs round: +16%

2 carat: Round length x width: 8.1 mm; Marquise length x width: 13.1 x 6.6 mm; Marquise face-up vs round: +16%

3 carat: Round length x width: 9.3 mm; Marquise length x width: 15.0 x 7.5 mm; Marquise face-up vs round: +16%

Carat	Round length x width	Marquise length x width	Marquise face-up vs round
0.5 carat	5.1 mm	8.3 x 4.1 mm	+16%
0.75 carat	5.9 mm	9.4 x 4.7 mm	+16%
1 carat	6.5 mm	10.4 x 5.2 mm	+16%
1.5 carat	7.4 mm	11.9 x 6.0 mm	+16%
2 carat	8.1 mm	13.1 x 6.6 mm	+16%
3 carat	9.3 mm	15.0 x 7.5 mm	+16%

Round vs Marquise on a finger

A 1 carat round covers 39% of the width of a size 6 finger and a 1 carat marquise covers 32%. Long cuts sit along the finger, so their width is what shows across it.

6.0 mm stone on a 16.5 mm finger: it covers 36% of the widthA 1.5 carat marquise on a size 6 finger.

4: Finger width: 14.9 mm; 1.5 ct round covers: 50%; 1.5 ct marquise covers: 40%

5: Finger width: 15.7 mm; 1.5 ct round covers: 47%; 1.5 ct marquise covers: 38%

6: Finger width: 16.5 mm; 1.5 ct round covers: 45%; 1.5 ct marquise covers: 36%

7: Finger width: 17.3 mm; 1.5 ct round covers: 43%; 1.5 ct marquise covers: 34%

8: Finger width: 18.1 mm; 1.5 ct round covers: 41%; 1.5 ct marquise covers: 33%

US ring size	Finger width	1.5 ct round covers	1.5 ct marquise covers
4	14.9 mm	50%	40%
5	15.7 mm	47%	38%
6	16.5 mm	45%	36%
7	17.3 mm	43%	34%
8	18.1 mm	41%	33%

Match the look, not only the carat

Because a marquise of about 0.80 carat faces up like 1 carat of round, comparing by weight alone hides the difference. Compare millimeters, or put both stones side by side in the size comparison tool.

Round and Marquise size charts

Full charts from 0.25 to 5 carat: Round diamond size chart and Marquise diamond size chart.

Questions

At the same weight a marquise faces up about 16% larger than a round. Face-up area is what you see from above; the marquise has more of it at equal weight.

A 1 carat round is about 6.5 mm and a 1 carat marquise about 10.4 x 5.2 mm, for a well-cut stone at the usual ratio.

A 2 carat round is 8.1 mm and a 2 carat marquise is 13.1 x 6.6 mm. Face-up, the marquise is +16% against the round.

A 1 carat round covers 39% of the width of a size 6 finger and a 1 carat marquise 32%. The numbers change with ring size and with the stone's length-to-width ratio.