How big is a 4 carat heart shaped diamond?

By HeyGema™ · Updated November 5, 2026

In short

A 4 carat heart shaped diamond measures about 10.3 x 10.3 mm. It faces up 17% smaller than a round diamond of the same weight. On a size 6 finger it covers 63% of the width. For the same weight, a round diamond is 10.2 mm.

10.3 x 10.3 mm4 carat heart
0.41 x 0.41 inthe same in inches
-17%face-up size vs a round
63%of a size 6 finger's width

Carat to mm calculator

ShapeGemCarat

About 10.3 x 10.3 mm

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

4 ct heart

10.3 x 10.3 mm

4 ct round

10.2 mm

Side by side

4 ct round inside 4 ct heart

A 4 carat heart diamond beside a 4 carat round, to the same scale.

4 carat heart diamond size

A well-cut 4 carat heart shaped diamond measures about 10.3 x 10.3 mm (0.41 x 0.41 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 0.80 grams.

4 carat heart on a finger

10.3 mm stone on a 16.5 mm finger: it covers 63% of the widthA 4 carat heart diamond on a size 6 finger.

4: Finger width: 14.9 mm; Heart covers: 69%

5: Finger width: 15.7 mm; Heart covers: 66%

6: Finger width: 16.5 mm; Heart covers: 63%

7: Finger width: 17.3 mm; Heart covers: 60%

8: Finger width: 18.1 mm; Heart covers: 57%

9: Finger width: 18.9 mm; Heart covers: 54%

US ring size	Finger width	Heart covers
4	14.9 mm	69%
5	15.7 mm	66%
6	16.5 mm	63%
7	17.3 mm	60%
8	18.1 mm	57%
9	18.9 mm	54%

Heart sizes near 4 carat

3 carat: Length x width: 9.4 x 9.4 mm; Round of the same weight: 9.3 mm

3.5 carat: Length x width: 9.9 x 9.9 mm; Round of the same weight: 9.8 mm

4 (this page): Length x width: 10.3 x 10.3 mm; Round of the same weight: 10.2 mm

5 carat: Length x width: 11.1 x 11.1 mm; Round of the same weight: 11.0 mm

6 carat: Length x width: 11.8 x 11.8 mm; Round of the same weight: 11.7 mm

Carat	Length x width	Round of the same weight
3 carat	9.4 x 9.4 mm	9.3 mm
3.5 carat	9.9 x 9.9 mm	9.8 mm
4 (this page)	10.3 x 10.3 mm	10.2 mm
5 carat	11.1 x 11.1 mm	11.0 mm
6 carat	11.8 x 11.8 mm	11.7 mm

4 carat in other shapes

Every row is a well-cut diamond of 4 carat. The last column is the face-up size against the heart.

Round: Length x width: 10.2 mm; Against heart: +21%

Oval: Length x width: 12.7 x 8.7 mm; Against heart: +28%

Cushion: Length x width: 8.9 x 8.9 mm; Against heart: +4%

Princess: Length x width: 8.7 x 8.7 mm; Against heart: +11%

Emerald cut: Length x width: 11.1 x 7.9 mm; Against heart: +25%

Asscher: Length x width: 8.7 x 8.7 mm; Against heart: +2%

Radiant: Length x width: 10.3 x 7.9 mm; Against heart: +18%

Pear: Length x width: 13.5 x 8.7 mm; Against heart: +17%

Marquise: Length x width: 16.5 x 8.3 mm; Against heart: +40%

Trillion: Length x width: 11.1 x 11.1 mm; Against heart: +4%

Baguette: Length x width: 12.7 x 6.3 mm; Against heart: +18%

Shape	Length x width	Against heart
Round	10.2 mm	+21%
Oval	12.7 x 8.7 mm	+28%
Cushion	8.9 x 8.9 mm	+4%
Princess	8.7 x 8.7 mm	+11%
Emerald cut	11.1 x 7.9 mm	+25%
Asscher	8.7 x 8.7 mm	+2%
Radiant	10.3 x 7.9 mm	+18%
Pear	13.5 x 8.7 mm	+17%
Marquise	16.5 x 8.3 mm	+40%
Trillion	11.1 x 11.1 mm	+4%
Baguette	12.7 x 6.3 mm	+18%

Questions

A 4 carat heart shaped diamond is about 10.3 x 10.3 mm at the usual 1.00:1 ratio.

No. Face-up, a 4 carat heart is 17% smaller than a 4 carat round (10.2 mm).

There is no rule. The stone is wider than most fingers. 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.