Round vs Asscher diamond size

By HeyGema™ · Updated November 5, 2026

In short

A 1 carat round measures 6.5 mm and a 1 carat asscher 5.5 x 5.5 mm. At the same weight a round faces up about 16% larger than an asscher. In face-up terms, 1 carat of round looks like a 1.00 carat round and 1 carat of asscher like a 0.78 carat round.

6.5 mm1 ct round
5.5 x 5.5 mm1 ct asscher
-16%asscher face-up vs round

Carat to mm calculator

ShapeGemCarat

About 5.5 x 5.5 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 asscher

5.5 x 5.5 mm

Side by side

1 ct asscher inside 1 ct round

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

Round vs Asscher diamond size at the same weight

At the same weight a round faces up about 16% larger than an asscher. A 1 carat round measures 6.5 mm and a 1 carat asscher 5.5 x 5.5 mm. A 1 carat round faces up like a 1.00 carat round, and a 1 carat asscher like a 0.78 carat round.

0.5 carat: Round length x width: 5.1 mm; Asscher length x width: 4.4 x 4.4 mm; Asscher face-up vs round: -16%

0.75 carat: Round length x width: 5.9 mm; Asscher length x width: 5.0 x 5.0 mm; Asscher face-up vs round: -16%

1 carat: Round length x width: 6.5 mm; Asscher length x width: 5.5 x 5.5 mm; Asscher face-up vs round: -16%

1.5 carat: Round length x width: 7.4 mm; Asscher length x width: 6.3 x 6.3 mm; Asscher face-up vs round: -16%

2 carat: Round length x width: 8.1 mm; Asscher length x width: 6.9 x 6.9 mm; Asscher face-up vs round: -16%

3 carat: Round length x width: 9.3 mm; Asscher length x width: 7.9 x 7.9 mm; Asscher face-up vs round: -16%

Carat	Round length x width	Asscher length x width	Asscher face-up vs round
0.5 carat	5.1 mm	4.4 x 4.4 mm	-16%
0.75 carat	5.9 mm	5.0 x 5.0 mm	-16%
1 carat	6.5 mm	5.5 x 5.5 mm	-16%
1.5 carat	7.4 mm	6.3 x 6.3 mm	-16%
2 carat	8.1 mm	6.9 x 6.9 mm	-16%
3 carat	9.3 mm	7.9 x 7.9 mm	-16%

Round vs Asscher on a finger

A 1 carat round covers 39% of the width of a size 6 finger and a 1 carat asscher covers 33%. Long cuts sit along the finger, so their width is what shows across it.

6.3 mm stone on a 16.5 mm finger: it covers 38% of the widthA 1.5 carat asscher on a size 6 finger.

4: Finger width: 14.9 mm; 1.5 ct round covers: 50%; 1.5 ct asscher covers: 42%

5: Finger width: 15.7 mm; 1.5 ct round covers: 47%; 1.5 ct asscher covers: 40%

6: Finger width: 16.5 mm; 1.5 ct round covers: 45%; 1.5 ct asscher covers: 38%

7: Finger width: 17.3 mm; 1.5 ct round covers: 43%; 1.5 ct asscher covers: 36%

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

US ring size	Finger width	1.5 ct round covers	1.5 ct asscher covers
4	14.9 mm	50%	42%
5	15.7 mm	47%	40%
6	16.5 mm	45%	38%
7	17.3 mm	43%	36%
8	18.1 mm	41%	35%

Match the look, not only the carat

Because an asscher needs about 1.29 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 Asscher size charts

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

Questions

At the same weight a round faces up about 16% larger than an asscher. 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 asscher about 5.5 x 5.5 mm, for a well-cut stone at the usual ratio.

A 2 carat round is 8.1 mm and a 2 carat asscher is 6.9 x 6.9 mm. Face-up, the asscher is -16% against the round.

A 1 carat round covers 39% of the width of a size 6 finger and a 1 carat asscher 33%. The numbers change with ring size and with the stone's length-to-width ratio.