Round vs Cushion diamond size

By HeyGema™ · Updated November 5, 2026

In short

A 1 carat round measures 6.5 mm and a 1 carat cushion 5.6 x 5.6 mm. At the same weight a round faces up about 14% larger than a cushion. In face-up terms, 1 carat of round looks like a 1.00 carat round and 1 carat of cushion like a 0.80 carat round.

6.5 mm1 ct round
5.6 x 5.6 mm1 ct cushion
-14%cushion face-up vs round

Carat to mm calculator

ShapeGemCaratLength to width

About 5.6 x 5.6 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 cushion

5.6 x 5.6 mm

Side by side

1 ct cushion inside 1 ct round

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

Round vs Cushion diamond size at the same weight

At the same weight a round faces up about 14% larger than a cushion. A 1 carat round measures 6.5 mm and a 1 carat cushion 5.6 x 5.6 mm. A 1 carat round faces up like a 1.00 carat round, and a 1 carat cushion like a 0.80 carat round.

0.5 carat: Round length x width: 5.1 mm; Cushion length x width: 4.4 x 4.4 mm; Cushion face-up vs round: -14%

0.75 carat: Round length x width: 5.9 mm; Cushion length x width: 5.1 x 5.1 mm; Cushion face-up vs round: -14%

1 carat: Round length x width: 6.5 mm; Cushion length x width: 5.6 x 5.6 mm; Cushion face-up vs round: -14%

1.5 carat: Round length x width: 7.4 mm; Cushion length x width: 6.4 x 6.4 mm; Cushion face-up vs round: -14%

2 carat: Round length x width: 8.1 mm; Cushion length x width: 7.1 x 7.1 mm; Cushion face-up vs round: -14%

3 carat: Round length x width: 9.3 mm; Cushion length x width: 8.1 x 8.1 mm; Cushion face-up vs round: -14%

Carat	Round length x width	Cushion length x width	Cushion face-up vs round
0.5 carat	5.1 mm	4.4 x 4.4 mm	-14%
0.75 carat	5.9 mm	5.1 x 5.1 mm	-14%
1 carat	6.5 mm	5.6 x 5.6 mm	-14%
1.5 carat	7.4 mm	6.4 x 6.4 mm	-14%
2 carat	8.1 mm	7.1 x 7.1 mm	-14%
3 carat	9.3 mm	8.1 x 8.1 mm	-14%

Round vs Cushion on a finger

A 1 carat round covers 39% of the width of a size 6 finger and a 1 carat cushion covers 34%. Long cuts sit along the finger, so their width is what shows across it.

6.4 mm stone on a 16.5 mm finger: it covers 39% of the widthA 1.5 carat cushion on a size 6 finger.

4: Finger width: 14.9 mm; 1.5 ct round covers: 50%; 1.5 ct cushion covers: 43%

5: Finger width: 15.7 mm; 1.5 ct round covers: 47%; 1.5 ct cushion covers: 41%

6: Finger width: 16.5 mm; 1.5 ct round covers: 45%; 1.5 ct cushion covers: 39%

7: Finger width: 17.3 mm; 1.5 ct round covers: 43%; 1.5 ct cushion covers: 37%

8: Finger width: 18.1 mm; 1.5 ct round covers: 41%; 1.5 ct cushion covers: 35%

US ring size	Finger width	1.5 ct round covers	1.5 ct cushion covers
4	14.9 mm	50%	43%
5	15.7 mm	47%	41%
6	16.5 mm	45%	39%
7	17.3 mm	43%	37%
8	18.1 mm	41%	35%

Match the look, not only the carat

Because a cushion needs about 1.26 carat to face 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 Cushion size charts

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

Questions

At the same weight a round faces up about 14% larger than a cushion. Face-up area is what you see from above; the round has more of it at equal weight.

A 1 carat round is about 6.5 mm and a 1 carat cushion about 5.6 x 5.6 mm, for a well-cut stone at the usual ratio.

A 2 carat round is 8.1 mm and a 2 carat cushion is 7.1 x 7.1 mm. Face-up, the cushion is -14% against the round.

A 1 carat round covers 39% of the width of a size 6 finger and a 1 carat cushion 34%. The numbers change with ring size and with the stone's length-to-width ratio.