How big is a 1.25 carat heart shaped diamond?

By HeyGema™ · Updated November 5, 2026

In short

A 1.25 carat heart shaped diamond measures about 7.0 x 7.0 mm. It faces up 17% smaller than a round diamond of the same weight. On a size 6 finger it covers 42% of the width. For the same weight, a round diamond is 6.9 mm.

7.0 x 7.0 mm1.25 carat heart
0.28 x 0.28 inthe same in inches
-17%face-up size vs a round
42%of a size 6 finger's width

Carat to mm calculator

ShapeGemCarat

About 7.0 x 7.0 mm

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

1.25 ct heart

7.0 x 7.0 mm

1.25 ct round

6.9 mm

Side by side

1.25 ct round inside 1.25 ct heart

A 1.25 carat heart diamond beside a 1.25 carat round, to the same scale.

1.25 carat heart diamond size

A well-cut 1.25 carat heart shaped diamond measures about 7.0 x 7.0 mm (0.28 x 0.28 inches) at a length-to-width ratio of 1.00:1. It faces up 17% smaller than a round diamond of the same weight. It weighs 0.25 grams.

1.25 carat heart on a finger

7.0 mm stone on a 16.5 mm finger: it covers 42% of the widthA 1.25 carat heart diamond on a size 6 finger.

4: Finger width: 14.9 mm; Heart covers: 47%

5: Finger width: 15.7 mm; Heart covers: 45%

6: Finger width: 16.5 mm; Heart covers: 42%

7: Finger width: 17.3 mm; Heart covers: 40%

8: Finger width: 18.1 mm; Heart covers: 39%

9: Finger width: 18.9 mm; Heart covers: 37%

US ring size	Finger width	Heart covers
4	14.9 mm	47%
5	15.7 mm	45%
6	16.5 mm	42%
7	17.3 mm	40%
8	18.1 mm	39%
9	18.9 mm	37%

Heart sizes near 1.25 carat

0.75 carat: Length x width: 5.9 x 5.9 mm; Round of the same weight: 5.9 mm

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

1.25 (this page): Length x width: 7.0 x 7.0 mm; Round of the same weight: 6.9 mm

1.5 carat: Length x width: 7.4 x 7.4 mm; Round of the same weight: 7.4 mm

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

Carat	Length x width	Round of the same weight
0.75 carat	5.9 x 5.9 mm	5.9 mm
1 carat	6.5 x 6.5 mm	6.5 mm
1.25 (this page)	7.0 x 7.0 mm	6.9 mm
1.5 carat	7.4 x 7.4 mm	7.4 mm
1.75 carat	7.8 x 7.8 mm	7.8 mm

1.25 carat in other shapes

Every row is a well-cut diamond of 1.25 carat. The last column is the face-up size against the heart.

Round: Length x width: 6.9 mm; Against heart: +21%

Oval: Length x width: 8.6 x 5.9 mm; Against heart: +28%

Cushion: Length x width: 6.0 x 6.0 mm; Against heart: +4%

Princess: Length x width: 5.9 x 5.9 mm; Against heart: +11%

Emerald cut: Length x width: 7.5 x 5.4 mm; Against heart: +25%

Asscher: Length x width: 5.9 x 5.9 mm; Against heart: +2%

Radiant: Length x width: 7.0 x 5.4 mm; Against heart: +18%

Pear: Length x width: 9.2 x 5.9 mm; Against heart: +17%

Marquise: Length x width: 11.2 x 5.6 mm; Against heart: +40%

Trillion: Length x width: 7.5 x 7.5 mm; Against heart: +4%

Baguette: Length x width: 8.6 x 4.3 mm; Against heart: +18%

Shape	Length x width	Against heart
Round	6.9 mm	+21%
Oval	8.6 x 5.9 mm	+28%
Cushion	6.0 x 6.0 mm	+4%
Princess	5.9 x 5.9 mm	+11%
Emerald cut	7.5 x 5.4 mm	+25%
Asscher	5.9 x 5.9 mm	+2%
Radiant	7.0 x 5.4 mm	+18%
Pear	9.2 x 5.9 mm	+17%
Marquise	11.2 x 5.6 mm	+40%
Trillion	7.5 x 7.5 mm	+4%
Baguette	8.6 x 4.3 mm	+18%

Questions

A 1.25 carat heart shaped diamond is about 7.0 x 7.0 mm at the usual 1.00:1 ratio.

No. Face-up, a 1.25 carat heart is 17% smaller than a 1.25 carat round (6.9 mm).

There is no rule. The stone is 47% of the width of a size 4 finger and 39% 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.