How big is a 1.5 carat round diamond?

By HeyGema™ · Updated November 5, 2026

In short

A 1.5 carat round diamond measures about 7.4 mm. On a size 6 finger it covers 45% of the width. For the same weight, a round diamond is 7.4 mm.

7.4 mm1.5 carat round
0.29 inthe same in inches
referenceface-up size vs a round
45%of a size 6 finger's width

Carat to mm calculator

ShapeGemCarat

About 7.4 x 7.4 mm

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

1.5 ct round

7.4 mm

1.5 ct round

7.4 mm

Side by side

1.5 ct round inside 1.5 ct round

A 1.5 carat round diamond beside a 1.5 carat round, to the same scale.

1.5 carat round diamond size

A well-cut 1.5 carat round diamond measures about 7.4 mm (0.29 inches) at a length-to-width ratio of 1.00:1. It weighs 0.30 grams.

1.5 carat round on a finger

7.4 mm stone on a 16.5 mm finger: it covers 45% of the widthA 1.5 carat round diamond on a size 6 finger.

4: Finger width: 14.9 mm; Round covers: 50%

5: Finger width: 15.7 mm; Round covers: 47%

6: Finger width: 16.5 mm; Round covers: 45%

7: Finger width: 17.3 mm; Round covers: 43%

8: Finger width: 18.1 mm; Round covers: 41%

9: Finger width: 18.9 mm; Round covers: 39%

US ring size	Finger width	Round covers
4	14.9 mm	50%
5	15.7 mm	47%
6	16.5 mm	45%
7	17.3 mm	43%
8	18.1 mm	41%
9	18.9 mm	39%

Round sizes near 1.5 carat

1 carat: Length x width: 6.5 mm; Round of the same weight: 6.5 mm

1.25 carat: Length x width: 6.9 mm; Round of the same weight: 6.9 mm

1.5 (this page): Length x width: 7.4 mm; Round of the same weight: 7.4 mm

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

Carat	Length x width	Round of the same weight
1 carat	6.5 mm	6.5 mm
1.25 carat	6.9 mm	6.9 mm
1.5 (this page)	7.4 mm	7.4 mm
1.75 carat	7.8 mm	7.8 mm
2 carat	8.1 mm	8.1 mm

1.5 carat in other shapes

Every row is a well-cut diamond of 1.5 carat. The last column is the face-up size against the round.

Oval: Length x width: 9.2 x 6.3 mm; Against round: +6%

Cushion: Length x width: 6.4 x 6.4 mm; Against round: -14%

Princess: Length x width: 6.3 x 6.3 mm; Against round: -8%

Emerald cut: Length x width: 8.0 x 5.7 mm; Against round: +4%

Asscher: Length x width: 6.3 x 6.3 mm; Against round: -16%

Radiant: Length x width: 7.4 x 5.7 mm; Against round: -2%

Pear: Length x width: 9.7 x 6.3 mm; Against round: -3%

Marquise: Length x width: 11.9 x 6.0 mm; Against round: +16%

Heart: Length x width: 7.4 x 7.4 mm; Against round: -17%

Trillion: Length x width: 8.0 x 8.0 mm; Against round: -14%

Baguette: Length x width: 9.2 x 4.6 mm; Against round: -2%

Shape	Length x width	Against round
Oval	9.2 x 6.3 mm	+6%
Cushion	6.4 x 6.4 mm	-14%
Princess	6.3 x 6.3 mm	-8%
Emerald cut	8.0 x 5.7 mm	+4%
Asscher	6.3 x 6.3 mm	-16%
Radiant	7.4 x 5.7 mm	-2%
Pear	9.7 x 6.3 mm	-3%
Marquise	11.9 x 6.0 mm	+16%
Heart	7.4 x 7.4 mm	-17%
Trillion	8.0 x 8.0 mm	-14%
Baguette	9.2 x 4.6 mm	-2%

Questions

A 1.5 carat round diamond is about 7.4 mm at the usual 1.00:1 ratio.

A 1.5 carat round diamond is about 0.29 inches across.

There is no rule. The stone is 50% of the width of a size 4 finger and 41% 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.