How big is a 100 carat diamond?
By HeyGema™ · Updated
In short
A 100 carat round diamond measures about 29.9 mm across (1.18 inches) and weighs 20.00 grams. An oval of the same weight is 37.1 x 25.5 mm and an emerald cut 32.5 x 23.2 mm. On a size 6 finger a round 100 carat covers 181% of the width.
- 29.9 mmround diamond, across
- 1.18 inthe same in inches
- 20.00 gweight
- 181%of a size 6 finger's width
Carat to mm calculator
About 29.9 x 29.9 mm
An estimate for a well-cut stone. A deep or shallow cut faces up smaller or bigger.
100 carat diamond size by shape
These are the face-up measurements of a well-cut 100 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: 29.9 mm
- In inches: 1.18 in
- Face-up size vs round: -
- Oval
- Length x width: 37.1 x 25.5 mm
- In inches: 1.46 x 1.01 in
- Face-up size vs round: +6%
- Cushion
- Length x width: 26.0 x 26.0 mm
- In inches: 1.02 x 1.02 in
- Face-up size vs round: -14%
- Princess
- Length x width: 25.5 x 25.5 mm
- In inches: 1.01 x 1.01 in
- Face-up size vs round: -8%
- Emerald cut
- Length x width: 32.5 x 23.2 mm
- In inches: 1.28 x 0.91 in
- Face-up size vs round: +4%
- Asscher
- Length x width: 25.5 x 25.5 mm
- In inches: 1.01 x 1.01 in
- Face-up size vs round: -16%
- Radiant
- Length x width: 30.2 x 23.2 mm
- In inches: 1.19 x 0.91 in
- Face-up size vs round: -2%
- Pear
- Length x width: 39.5 x 25.5 mm
- In inches: 1.55 x 1.01 in
- Face-up size vs round: -3%
- Marquise
- Length x width: 48.3 x 24.1 mm
- In inches: 1.90 x 0.95 in
- Face-up size vs round: +16%
- Heart
- Length x width: 30.2 x 30.2 mm
- In inches: 1.19 x 1.19 in
- Face-up size vs round: -17%
- Trillion
- Length x width: 32.5 x 32.5 mm
- In inches: 1.28 x 1.28 in
- Face-up size vs round: -14%
- Baguette
- Length x width: 37.1 x 18.6 mm
- In inches: 1.46 x 0.73 in
- Face-up size vs round: -2%
100 carat diamond next to a coin
Is a 100 carat diamond big?
It depends on the hand. A round 100 carat covers 201% of the width of a size 4 finger, 181% of a size 6 and 165% of a size 8. At 100 carats a round diamond is 29.9 mm across, about as wide as a US half dollar (30.61 mm). A stone this size is usually worn as a pendant or made into a piece for it, not set in a ring.
100 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: 201%
- Oval: 172%
- Cushion: 175%
- Emerald cut: 156%
- 5
- Finger width: 15.7 mm
- Round: 191%
- Oval: 163%
- Cushion: 166%
- Emerald cut: 148%
- 6
- Finger width: 16.5 mm
- Round: 181%
- Oval: 155%
- Cushion: 157%
- Emerald cut: 141%
- 7
- Finger width: 17.3 mm
- Round: 173%
- Oval: 147%
- Cushion: 150%
- Emerald cut: 134%
- 8
- Finger width: 18.1 mm
- Round: 165%
- Oval: 141%
- Cushion: 143%
- Emerald cut: 128%
- 9
- Finger width: 18.9 mm
- Round: 158%
- Oval: 135%
- Cushion: 137%
- Emerald cut: 123%
100 carat compared with nearby sizes
Round diamond diameter for the weights on either side of 100 carat. The last column is the difference in width from a 100 carat stone.
- 50 carat
- Round diameter: 23.8 mm
- Difference from 100 ct: -6.18 mm
- 75 carat
- Round diameter: 27.2 mm
- Difference from 100 ct: -2.74 mm
- 100 (this page)
- Round diameter: 29.9 mm
- Difference from 100 ct: -
Other gems at 100 carat
Gems are not all as dense as diamond, so the same weight faces up bigger or smaller. Round stones of 100 carat:
- Diamond
- Round diameter: 29.9 mm
- Against diamond: -
- Moissanite
- Round diameter: 30.8 mm
- Against diamond: +3% wider
- Sapphire
- Round diameter: 28.7 mm
- Against diamond: -4% wider
- Ruby
- Round diameter: 28.7 mm
- Against diamond: -4% wider
- Emerald
- Round diameter: 32.6 mm
- Against diamond: +9% wider
- Aquamarine
- Round diameter: 32.7 mm
- Against diamond: +9% wider
- Morganite
- Round diameter: 32.3 mm
- Against diamond: +8% wider
- Tanzanite
- Round diameter: 30.4 mm
- Against diamond: +2% wider
- Topaz
- Round diameter: 29.9 mm
- Against diamond: same
- Amethyst
- Round diameter: 32.9 mm
- Against diamond: +10% wider
- Spinel
- Round diameter: 29.7 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.