Stone Guide

Diamond Carat Size Chart: Millimetres to Carats

This diamond size chart converts the diameter of a round stone, in millimetres, into its approximate carat weight, from 0.9 mm to 11 mm. Use it to choose a stone size for a ring, a pendant or any other piece you plan to have made at Atelier KBS in Tunis.

Carat measures weight, not size: two stones of the same weight can look slightly different depending on their cut and proportions, so treat these values as a guide. The unit conversions are at the bottom of the page.

Looking to have stones set? See our stone setting service and the quality control checks done before shipping.

Diagram of stone shapes: pear, oval, baguette

Diameter (mm)	Carat Weight
4 mm	0.25 ct
5.0 mm	0.50 ct
5.75 mm	0.75 ct
6.5 mm	1.00 ct
6.8 mm	1.25 ct
7.3 mm	1.50 ct
7.75 mm	1.75 ct
8 mm	2.00 ct
8.7 mm	2.50 ct
9.1 mm	3.00 ct
9.75 mm	3.50 ct
10.25 mm	4.00 ct
10.75 mm	4.50 ct
11 mm	5.00 ct

Hand wearing rings with different diamond sizes

View Full Chart

Round Cut

Diameter (mm)	Carat Weight
0.9	0.004
1	0.005
1.1	0.0067
1.2	0.0075
1.25	0.0089
1.3	0.01
1.4	0.012
1.5	0.015
1.7	0.02
1.75	0.025
1.8	0.025
2	0.03
2.1	0.035
2.2	0.04
2.25	0.04
2.4	0.05
2.5	0.06
2.75	0.07
2.8	0.08
2.9	0.09
3	0.1
3.1	0.11
3.25	0.12
3.3	0.14
3.4	0.15
3.5	0.16
3.6	0.17
3.75	0.19
3.8	0.2
3.9	0.22
4	0.23
4.1	0.25
4.2	0.3
4.25	0.315
4.4	0.33

Diameter (mm)	Carat Weight
4.5	0.35
4.6	0.38
4.8	0.4
5	0.5
5.4	0.6
5.5	0.63
5.6	0.65
5.8	0.75
6	0.8
6.4	0.95
6.5	1
6.6	1.1
6.8	1.17
7	1.25
7.2	1.33
7.4	1.5
7.5	1.55
7.6	1.6
7.8	1.75
8	2
8.4	2.15
8.5	2.25
8.6	2.35
8.8	2.5
9	2.75
9.2	2.85
9.4	3
9.6	3.15
9.8	3.35
10	3.5
10.2	3.75
10.4	4
10.6	4.25

Values are approximate for well-cut round diamonds; the actual weight depends on the proportions of the stone.

Carat Weight

Carat is the unit of measurement used to weigh precious and semi-precious stones
1 carat	= 0.20 grammes
1 gramme	= 5 carats
1 carat	= 100 points