How many carats is a 4 mm diamond?

By HeyGema™ · Updated November 5, 2026

In short

A 4 mm round diamond weighs about 0.24 carat (0.048 grams). A 4 mm princess cut weighs about 0.38 carat, and an oval that is 4 mm long about 0.13 carat.

0.24 ctround diamond, 4 mm
0.048 gweight
0.16 in4 mm in inches

Carat to mm calculator

ShapeGemLength (mm)

About 0.24 carat

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

4 mm diamond weight by shape

The weight of a well-cut diamond measuring 4 mm. For round and square shapes the number is the diameter or the side. For longer shapes it is the long side, with the width following the usual ratio.

Round: Size: 4 mm; Weight: 0.24 ct

Oval: Size: 4 mm x 2.76 mm; Weight: 0.13 ct

Cushion: Size: 4 mm x 4.0 mm; Weight: 0.36 ct

Princess: Size: 4 mm x 4.0 mm; Weight: 0.38 ct

Emerald cut: Size: 4 mm x 2.86 mm; Weight: 0.19 ct

Asscher: Size: 4 mm x 4.0 mm; Weight: 0.38 ct

Radiant: Size: 4 mm x 3.1 mm; Weight: 0.23 ct

Pear: Size: 4 mm x 2.58 mm; Weight: 0.1 ct

Marquise: Size: 4 mm x 2.00 mm; Weight: 0.060 ct

Heart: Size: 4 mm x 4.0 mm; Weight: 0.23 ct

Trillion: Size: 4 mm x 4.0 mm; Weight: 0.19 ct

Baguette: Size: 4 mm x 2.00 mm; Weight: 0.13 ct

Shape	Size	Weight
Round	4 mm	0.24 ct
Oval	4 mm x 2.76 mm	0.13 ct
Cushion	4 mm x 4.0 mm	0.36 ct
Princess	4 mm x 4.0 mm	0.38 ct
Emerald cut	4 mm x 2.86 mm	0.19 ct
Asscher	4 mm x 4.0 mm	0.38 ct
Radiant	4 mm x 3.1 mm	0.23 ct
Pear	4 mm x 2.58 mm	0.1 ct
Marquise	4 mm x 2.00 mm	0.060 ct
Heart	4 mm x 4.0 mm	0.23 ct
Trillion	4 mm x 4.0 mm	0.19 ct
Baguette	4 mm x 2.00 mm	0.13 ct

4 mm stones in other gems

A round stone of the same size weighs differently in each gem, because gems differ in density.

Diamond: Weight of a round stone: 0.24 ct

Moissanite: Weight of a round stone: 0.22 ct

Sapphire: Weight of a round stone: 0.27 ct

Ruby: Weight of a round stone: 0.27 ct

Emerald: Weight of a round stone: 0.18 ct

Aquamarine: Weight of a round stone: 0.18 ct

Topaz: Weight of a round stone: 0.24 ct

Amethyst: Weight of a round stone: 0.18 ct

Spinel: Weight of a round stone: 0.24 ct

Tanzanite: Weight of a round stone: 0.23 ct

Morganite: Weight of a round stone: 0.19 ct

Gem	Weight of a round stone
Diamond	0.24 ct
Moissanite	0.22 ct
Sapphire	0.27 ct
Ruby	0.27 ct
Emerald	0.18 ct
Aquamarine	0.18 ct
Topaz	0.24 ct
Amethyst	0.18 ct
Spinel	0.24 ct
Tanzanite	0.23 ct
Morganite	0.19 ct

4 mm diamond studs

A pair of 4 mm round diamond studs has a total carat weight of about 0.48 carat, 0.24 carat for each stone. See the diamond stud earring size chart.

Nearby sizes

3 mm: Weight: 0.1 ct; Inches: 0.12 in

3.5 mm: Weight: 0.16 ct; Inches: 0.14 in

4 mm (this page): Weight: 0.24 ct; Inches: 0.16 in

4.5 mm: Weight: 0.34 ct; Inches: 0.18 in

5 mm: Weight: 0.47 ct; Inches: 0.20 in

Diameter	Weight	Inches
3 mm	0.1 ct	0.12 in
3.5 mm	0.16 ct	0.14 in
4 mm (this page)	0.24 ct	0.16 in
4.5 mm	0.34 ct	0.18 in
5 mm	0.47 ct	0.20 in

Questions

About 0.24 carat for a well-cut round diamond.

A 4 mm princess cut, measured along one side, weighs about 0.38 carat.

A 4 mm round moissanite is labeled 0.24 carat (diamond equivalent weight) and weighs about 0.22 carat. See the moissanite size chart.

4 mm is 0.16 inches.