How big is a 0.25 carat princess cut diamond?

By HeyGema™ · Updated November 5, 2026

In short

A 0.25 carat princess cut diamond measures about 3.5 x 3.5 mm. It faces up 8% smaller than a round diamond of the same weight. On a size 6 finger it covers 21% of the width. For the same weight, a round diamond is 4.1 mm.

3.5 x 3.5 mm0.25 carat princess
0.14 x 0.14 inthe same in inches
-8%face-up size vs a round
21%of a size 6 finger's width

Carat to mm calculator

ShapeGemCarat

About 3.5 x 3.5 mm

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

0.25 ct princess

3.5 x 3.5 mm

0.25 ct round

4.1 mm

Side by side

0.25 ct princess inside 0.25 ct round

A 0.25 carat princess diamond beside a 0.25 carat round, to the same scale.

0.25 carat princess diamond size

A well-cut 0.25 carat princess cut diamond measures about 3.5 x 3.5 mm (0.14 x 0.14 inches) at a length-to-width ratio of 1.00:1. It faces up 8% smaller than a round diamond of the same weight. It weighs 0.050 grams.

0.25 carat princess on a finger

3.5 mm stone on a 16.5 mm finger: it covers 21% of the widthA 0.25 carat princess diamond on a size 6 finger.

4: Finger width: 14.9 mm; Princess covers: 23%

5: Finger width: 15.7 mm; Princess covers: 22%

6: Finger width: 16.5 mm; Princess covers: 21%

7: Finger width: 17.3 mm; Princess covers: 20%

8: Finger width: 18.1 mm; Princess covers: 19%

9: Finger width: 18.9 mm; Princess covers: 18%

US ring size	Finger width	Princess covers
4	14.9 mm	23%
5	15.7 mm	22%
6	16.5 mm	21%
7	17.3 mm	20%
8	18.1 mm	19%
9	18.9 mm	18%

Princess sizes near 0.25 carat

0.25 (this page): Length x width: 3.5 x 3.5 mm; Round of the same weight: 4.1 mm

0.33 carat: Length x width: 3.8 x 3.8 mm; Round of the same weight: 4.5 mm

0.5 carat: Length x width: 4.4 x 4.4 mm; Round of the same weight: 5.1 mm

Carat	Length x width	Round of the same weight
0.25 (this page)	3.5 x 3.5 mm	4.1 mm
0.33 carat	3.8 x 3.8 mm	4.5 mm
0.5 carat	4.4 x 4.4 mm	5.1 mm

0.25 carat in other shapes

Every row is a well-cut diamond of 0.25 carat. The last column is the face-up size against the princess.

Round: Length x width: 4.1 mm; Against princess: +9%

Oval: Length x width: 5.0 x 3.5 mm; Against princess: +15%

Cushion: Length x width: 3.5 x 3.5 mm; Against princess: -6%

Emerald cut: Length x width: 4.4 x 3.1 mm; Against princess: +13%

Asscher: Length x width: 3.5 x 3.5 mm; Against princess: -8%

Radiant: Length x width: 4.1 x 3.1 mm; Against princess: +6%

Pear: Length x width: 5.4 x 3.5 mm; Against princess: +6%

Marquise: Length x width: 6.6 x 3.3 mm; Against princess: +26%

Heart: Length x width: 4.1 x 4.1 mm; Against princess: -10%

Trillion: Length x width: 4.4 x 4.4 mm; Against princess: -6%

Baguette: Length x width: 5.0 x 2.52 mm; Against princess: +7%

Shape	Length x width	Against princess
Round	4.1 mm	+9%
Oval	5.0 x 3.5 mm	+15%
Cushion	3.5 x 3.5 mm	-6%
Emerald cut	4.4 x 3.1 mm	+13%
Asscher	3.5 x 3.5 mm	-8%
Radiant	4.1 x 3.1 mm	+6%
Pear	5.4 x 3.5 mm	+6%
Marquise	6.6 x 3.3 mm	+26%
Heart	4.1 x 4.1 mm	-10%
Trillion	4.4 x 4.4 mm	-6%
Baguette	5.0 x 2.52 mm	+7%

Questions

A 0.25 carat princess cut diamond is about 3.5 x 3.5 mm at the usual 1.00:1 ratio.

No. Face-up, a 0.25 carat princess is 8% smaller than a 0.25 carat round (4.1 mm).

There is no rule. The stone is 23% of the width of a size 4 finger and 19% 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.