How big is a 5 carat trillion cut diamond?

By HeyGema™ · Updated November 5, 2026

In short

A 5 carat trillion cut diamond measures about 12.0 x 12.0 mm. It faces up 14% smaller than a round diamond of the same weight. On a size 6 finger it covers 73% of the width. For the same weight, a round diamond is 11.0 mm.

12.0 x 12.0 mm5 carat trillion
0.47 x 0.47 inthe same in inches
-14%face-up size vs a round
73%of a size 6 finger's width

Carat to mm calculator

ShapeGemCarat

About 12.0 x 12.0 mm

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

5 ct trillion

12.0 x 12.0 mm

5 ct round

11.0 mm

Side by side

5 ct round inside 5 ct trillion

A 5 carat trillion diamond beside a 5 carat round, to the same scale.

5 carat trillion diamond size

A well-cut 5 carat trillion cut diamond measures about 12.0 x 12.0 mm (0.47 x 0.47 inches) at a length-to-width ratio of 1.00:1. It faces up 14% smaller than a round diamond of the same weight. It weighs 1.00 grams.

5 carat trillion on a finger

12.0 mm stone on a 16.5 mm finger: it covers 73% of the widthA 5 carat trillion diamond on a size 6 finger.

4: Finger width: 14.9 mm; Trillion covers: 80%

5: Finger width: 15.7 mm; Trillion covers: 76%

6: Finger width: 16.5 mm; Trillion covers: 73%

7: Finger width: 17.3 mm; Trillion covers: 69%

8: Finger width: 18.1 mm; Trillion covers: 66%

9: Finger width: 18.9 mm; Trillion covers: 63%

US ring size	Finger width	Trillion covers
4	14.9 mm	80%
5	15.7 mm	76%
6	16.5 mm	73%
7	17.3 mm	69%
8	18.1 mm	66%
9	18.9 mm	63%

Trillion sizes near 5 carat

3.5 carat: Length x width: 10.6 x 10.6 mm; Round of the same weight: 9.8 mm

4 carat: Length x width: 11.1 x 11.1 mm; Round of the same weight: 10.2 mm

5 (this page): Length x width: 12.0 x 12.0 mm; Round of the same weight: 11.0 mm

6 carat: Length x width: 12.7 x 12.7 mm; Round of the same weight: 11.7 mm

8 carat: Length x width: 14.0 x 14.0 mm; Round of the same weight: 12.9 mm

Carat	Length x width	Round of the same weight
3.5 carat	10.6 x 10.6 mm	9.8 mm
4 carat	11.1 x 11.1 mm	10.2 mm
5 (this page)	12.0 x 12.0 mm	11.0 mm
6 carat	12.7 x 12.7 mm	11.7 mm
8 carat	14.0 x 14.0 mm	12.9 mm

5 carat in other shapes

Every row is a well-cut diamond of 5 carat. The last column is the face-up size against the trillion.

Round: Length x width: 11.0 mm; Against trillion: +16%

Oval: Length x width: 13.7 x 9.4 mm; Against trillion: +22%

Cushion: Length x width: 9.6 x 9.6 mm; Against trillion: -1%

Princess: Length x width: 9.4 x 9.4 mm; Against trillion: +6%

Emerald cut: Length x width: 12.0 x 8.5 mm; Against trillion: +20%

Asscher: Length x width: 9.4 x 9.4 mm; Against trillion: -2%

Radiant: Length x width: 11.1 x 8.5 mm; Against trillion: +13%

Pear: Length x width: 14.5 x 9.4 mm; Against trillion: +12%

Marquise: Length x width: 17.8 x 8.9 mm; Against trillion: +34%

Heart: Length x width: 11.1 x 11.1 mm; Against trillion: -4%

Baguette: Length x width: 13.7 x 6.8 mm; Against trillion: +13%

Shape	Length x width	Against trillion
Round	11.0 mm	+16%
Oval	13.7 x 9.4 mm	+22%
Cushion	9.6 x 9.6 mm	-1%
Princess	9.4 x 9.4 mm	+6%
Emerald cut	12.0 x 8.5 mm	+20%
Asscher	9.4 x 9.4 mm	-2%
Radiant	11.1 x 8.5 mm	+13%
Pear	14.5 x 9.4 mm	+12%
Marquise	17.8 x 8.9 mm	+34%
Heart	11.1 x 11.1 mm	-4%
Baguette	13.7 x 6.8 mm	+13%

Questions

A 5 carat trillion cut diamond is about 12.0 x 12.0 mm at the usual 1.00:1 ratio.

No. Face-up, a 5 carat trillion is 14% smaller than a 5 carat round (11.0 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.