How big is a 8 carat diamond?
By HeyGema™ · Updated
In short
A 8 carat round diamond measures about 12.9 mm across (0.51 inches) and weighs 1.60 grams. An oval of the same weight is 16.0 x 11.0 mm and an emerald cut 14.0 x 10.0 mm. On a size 6 finger a round 8 carat covers 78% of the width. Pick a shape in the first table for its own 8 carat chart.
- 12.9 mmround diamond, across
- 0.51 inthe same in inches
- 1.60 gweight
- 78%of a size 6 finger's width
Carat to mm calculator
About 12.9 x 12.9 mm
An estimate for a well-cut stone. A deep or shallow cut faces up smaller or bigger.
8 carat diamond size by shape
These are the face-up measurements of a well-cut 8 carat diamond. Weight is the same in every row, but the face-up size is not: the last column compares each cut with a round diamond of the same weight.
- Round
- Length x width: 12.9 mm
- In inches: 0.51 in
- Face-up size vs round: -
- Oval
- Length x width: 16.0 x 11.0 mm
- In inches: 0.63 x 0.43 in
- Face-up size vs round: +6%
- Cushion
- Length x width: 11.2 x 11.2 mm
- In inches: 0.44 x 0.44 in
- Face-up size vs round: -14%
- Princess
- Length x width: 11.0 x 11.0 mm
- In inches: 0.43 x 0.43 in
- Face-up size vs round: -8%
- Emerald cut
- Length x width: 14.0 x 10.0 mm
- In inches: 0.55 x 0.39 in
- Face-up size vs round: +4%
- Asscher
- Length x width: 11.0 x 11.0 mm
- In inches: 0.43 x 0.43 in
- Face-up size vs round: -16%
- Radiant
- Length x width: 13.0 x 10.0 mm
- In inches: 0.51 x 0.39 in
- Face-up size vs round: -2%
- Pear
- Length x width: 17.0 x 11.0 mm
- In inches: 0.67 x 0.43 in
- Face-up size vs round: -3%
- Marquise
- Length x width: 20.8 x 10.4 mm
- In inches: 0.82 x 0.41 in
- Face-up size vs round: +16%
- Heart
- Length x width: 13.0 x 13.0 mm
- In inches: 0.51 x 0.51 in
- Face-up size vs round: -17%
- Trillion
- Length x width: 14.0 x 14.0 mm
- In inches: 0.55 x 0.55 in
- Face-up size vs round: -14%
- Baguette
- Length x width: 16.0 x 8.0 mm
- In inches: 0.63 x 0.31 in
- Face-up size vs round: -2%
8 carat diamond next to a coin
Is a 8 carat diamond big?
It depends on the hand. A round 8 carat covers 87% of the width of a size 4 finger, 78% of a size 6 and 71% of a size 8. Above 5 carats the stone is wider than half of a finger and needs a setting made for its size. At 12.9 mm across, a round 8 carat is 72% of the width of a US dime (17.91 mm).
8 carat diamond on a finger, by ring size
The share of the finger's width that the stone covers, for the four most searched shapes. Elongated stones sit along the finger, so their width is what you see across it. Try other ring sizes in the diamond size on finger tool.
- 4
- Finger width: 14.9 mm
- Round: 87%
- Oval: 74%
- Cushion: 75%
- Emerald cut: 67%
- 5
- Finger width: 15.7 mm
- Round: 82%
- Oval: 70%
- Cushion: 71%
- Emerald cut: 64%
- 6
- Finger width: 16.5 mm
- Round: 78%
- Oval: 67%
- Cushion: 68%
- Emerald cut: 61%
- 7
- Finger width: 17.3 mm
- Round: 74%
- Oval: 64%
- Cushion: 65%
- Emerald cut: 58%
- 8
- Finger width: 18.1 mm
- Round: 71%
- Oval: 61%
- Cushion: 62%
- Emerald cut: 55%
- 9
- Finger width: 18.9 mm
- Round: 68%
- Oval: 58%
- Cushion: 59%
- Emerald cut: 53%
8 carat compared with nearby sizes
Round diamond diameter for the weights on either side of 8 carat. The last column is the difference in width from a 8 carat stone.
- 6 carat
- Round diameter: 11.7 mm
- Difference from 8 ct: -1.18 mm
- 7 carat
- Round diameter: 12.3 mm
- Difference from 8 ct: -0.56 mm
- 8 (this page)
- Round diameter: 12.9 mm
- Difference from 8 ct: -
- 9 carat
- Round diameter: 13.4 mm
- Difference from 8 ct: +0.52 mm
- 10 carat
- Round diameter: 13.9 mm
- Difference from 8 ct: +1.00 mm
Other gems at 8 carat
Gems are not all as dense as diamond, so the same weight faces up bigger or smaller. Round stones of 8 carat:
- Diamond
- Round diameter: 12.9 mm
- Against diamond: -
- Moissanite
- Round diameter: 13.3 mm
- Against diamond: +3% wider
- Sapphire
- Round diameter: 12.4 mm
- Against diamond: -4% wider
- Ruby
- Round diameter: 12.4 mm
- Against diamond: -4% wider
- Emerald
- Round diameter: 14.1 mm
- Against diamond: +9% wider
- Aquamarine
- Round diameter: 14.1 mm
- Against diamond: +9% wider
- Morganite
- Round diameter: 13.9 mm
- Against diamond: +8% wider
- Tanzanite
- Round diameter: 13.1 mm
- Against diamond: +2% wider
- Topaz
- Round diameter: 12.9 mm
- Against diamond: same
- Amethyst
- Round diameter: 14.2 mm
- Against diamond: +10% wider
- Spinel
- Round diameter: 12.8 mm
- Against diamond: -1% wider
How these sizes are worked out
We start from the face-up size of a well-cut 1 carat diamond of each shape and scale it with the cube root of the weight and the gem's density. They are estimates for a typical cut. See the methodology for the formulas, or use the calculator above for any weight.