How big is a 2.25 carat round diamond?

By HeyGema™ · Updated November 5, 2026

In short

A 2.25 carat round diamond measures about 8.5 mm. On a size 6 finger it covers 51% of the width. For the same weight, a round diamond is 8.5 mm.

8.5 mm2.25 carat round
0.33 inthe same in inches
referenceface-up size vs a round
51%of a size 6 finger's width

Carat to mm calculator

ShapeGemCarat

About 8.5 x 8.5 mm

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

2.25 ct round

8.5 mm

2.25 ct round

8.5 mm

Side by side

2.25 ct round inside 2.25 ct round

A 2.25 carat round diamond beside a 2.25 carat round, to the same scale.

2.25 carat round diamond size

A well-cut 2.25 carat round diamond measures about 8.5 mm (0.33 inches) at a length-to-width ratio of 1.00:1. It weighs 0.45 grams.

2.25 carat round on a finger

8.5 mm stone on a 16.5 mm finger: it covers 51% of the widthA 2.25 carat round diamond on a size 6 finger.

4: Finger width: 14.9 mm; Round covers: 57%

5: Finger width: 15.7 mm; Round covers: 54%

6: Finger width: 16.5 mm; Round covers: 51%

7: Finger width: 17.3 mm; Round covers: 49%

8: Finger width: 18.1 mm; Round covers: 47%

9: Finger width: 18.9 mm; Round covers: 45%

US ring size	Finger width	Round covers
4	14.9 mm	57%
5	15.7 mm	54%
6	16.5 mm	51%
7	17.3 mm	49%
8	18.1 mm	47%
9	18.9 mm	45%

Round sizes near 2.25 carat

1.75 carat: Length x width: 7.8 mm; Round of the same weight: 7.8 mm

2 carat: Length x width: 8.1 mm; Round of the same weight: 8.1 mm

2.25 (this page): Length x width: 8.5 mm; Round of the same weight: 8.5 mm

2.5 carat: Length x width: 8.8 mm; Round of the same weight: 8.8 mm

3 carat: Length x width: 9.3 mm; Round of the same weight: 9.3 mm

Carat	Length x width	Round of the same weight
1.75 carat	7.8 mm	7.8 mm
2 carat	8.1 mm	8.1 mm
2.25 (this page)	8.5 mm	8.5 mm
2.5 carat	8.8 mm	8.8 mm
3 carat	9.3 mm	9.3 mm

2.25 carat in other shapes

Every row is a well-cut diamond of 2.25 carat. The last column is the face-up size against the round.

Oval: Length x width: 10.5 x 7.2 mm; Against round: +6%

Cushion: Length x width: 7.3 x 7.3 mm; Against round: -14%

Princess: Length x width: 7.2 x 7.2 mm; Against round: -8%

Emerald cut: Length x width: 9.2 x 6.6 mm; Against round: +4%

Asscher: Length x width: 7.2 x 7.2 mm; Against round: -16%

Radiant: Length x width: 8.5 x 6.6 mm; Against round: -2%

Pear: Length x width: 11.1 x 7.2 mm; Against round: -3%

Marquise: Length x width: 13.6 x 6.8 mm; Against round: +16%

Heart: Length x width: 8.5 x 8.5 mm; Against round: -17%

Trillion: Length x width: 9.2 x 9.2 mm; Against round: -14%

Baguette: Length x width: 10.5 x 5.2 mm; Against round: -2%

Shape	Length x width	Against round
Oval	10.5 x 7.2 mm	+6%
Cushion	7.3 x 7.3 mm	-14%
Princess	7.2 x 7.2 mm	-8%
Emerald cut	9.2 x 6.6 mm	+4%
Asscher	7.2 x 7.2 mm	-16%
Radiant	8.5 x 6.6 mm	-2%
Pear	11.1 x 7.2 mm	-3%
Marquise	13.6 x 6.8 mm	+16%
Heart	8.5 x 8.5 mm	-17%
Trillion	9.2 x 9.2 mm	-14%
Baguette	10.5 x 5.2 mm	-2%

Questions

A 2.25 carat round diamond is about 8.5 mm at the usual 1.00:1 ratio.

A 2.25 carat round diamond is about 0.33 inches across.

There is no rule. The stone is 57% of the width of a size 4 finger and 47% of a size 8. Compare it with a ring you have tried on in the finger chart above.

Yes. A lab grown diamond has the same density as a mined one, so it measures the same for the same weight.