How big is a 3.5 carat cushion cut diamond?

By HeyGema™ · Updated

In short

A 3.5 carat cushion cut diamond measures about 8.5 x 8.5 mm. It faces up 14% smaller than a round diamond of the same weight. On a size 6 finger it covers 52% of the width. For the same weight, a round diamond is 9.8 mm.

Carat to mm calculator

About 8.5 x 8.5 mm

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

3.5 ct cushion
8.5 x 8.5 mm
3.5 ct round
9.8 mm
Side by side
3.5 ct cushion inside 3.5 ct round
A 3.5 carat cushion diamond beside a 3.5 carat round, to the same scale.

3.5 carat cushion diamond size

A well-cut 3.5 carat cushion cut diamond measures about 8.5 x 8.5 mm (0.33 x 0.33 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 0.70 grams.

3.5 carat cushion size by length-to-width ratio

The same weight can be long and narrow or short and wide. These are 3.5 carat sizes at each ratio. A longer ratio runs the stone along the finger and makes it look slimmer. The face-up area stays almost the same.

1.00:1
Length x width: 8.5 x 8.5 mm
Width on the finger: 52% of a size 6 finger
1.10:1
Length x width: 8.9 x 8.1 mm
Width on the finger: 49% of a size 6 finger
1.20:1
Length x width: 9.3 x 7.8 mm
Width on the finger: 47% of a size 6 finger
1.30:1
Length x width: 9.7 x 7.5 mm
Width on the finger: 45% of a size 6 finger

3.5 carat cushion on a finger

8.5 mm
8.5 mm stone on a 16.5 mm finger: it covers 52% of the widthA 3.5 carat cushion diamond on a size 6 finger.
4
Finger width: 14.9 mm
Cushion covers: 57%
5
Finger width: 15.7 mm
Cushion covers: 54%
6
Finger width: 16.5 mm
Cushion covers: 52%
7
Finger width: 17.3 mm
Cushion covers: 49%
8
Finger width: 18.1 mm
Cushion covers: 47%
9
Finger width: 18.9 mm
Cushion covers: 45%

Cushion sizes near 3.5 carat

2.5 carat
Length x width: 7.6 x 7.6 mm
Round of the same weight: 8.8 mm
3 carat
Length x width: 8.1 x 8.1 mm
Round of the same weight: 9.3 mm
3.5 (this page)
Length x width: 8.5 x 8.5 mm
Round of the same weight: 9.8 mm
4 carat
Length x width: 8.9 x 8.9 mm
Round of the same weight: 10.2 mm
5 carat
Length x width: 9.6 x 9.6 mm
Round of the same weight: 11.0 mm

3.5 carat in other shapes

Every row is a well-cut diamond of 3.5 carat. The last column is the face-up size against the cushion.

Round
Length x width: 9.8 mm
Against cushion: +16%
Oval
Length x width: 12.1 x 8.4 mm
Against cushion: +23%
Princess
Length x width: 8.4 x 8.4 mm
Against cushion: +7%
Emerald cut
Length x width: 10.6 x 7.6 mm
Against cushion: +21%
Asscher
Length x width: 8.4 x 8.4 mm
Against cushion: -2%
Radiant
Length x width: 9.9 x 7.6 mm
Against cushion: +14%
Pear
Length x width: 12.9 x 8.4 mm
Against cushion: +13%
Marquise
Length x width: 15.8 x 7.9 mm
Against cushion: +35%
Heart
Length x width: 9.9 x 9.9 mm
Against cushion: -4%
Trillion
Length x width: 10.6 x 10.6 mm
Against cushion: +1%
Baguette
Length x width: 12.1 x 6.1 mm
Against cushion: +14%

Questions

A 3.5 carat cushion cut diamond is about 8.5 x 8.5 mm at the usual 1.00:1 ratio.
No. Face-up, a 3.5 carat cushion is 14% smaller than a 3.5 carat round (9.8 mm).
There is no rule. The stone is 57% of the width of a size 4 finger and 47% 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.

More size charts