MM to Carat Conversion Chart for Lab Grown Diamonds

When choosing a diamond, its size and weight are closely connected, but they are not the same thing. Carat refers to a diamond's weight, while millimetres describe its physical dimensions. A diamond's visible size can vary even when two stones have the same carat weight, depending on its shape and proportions.

This is where a millimetre to carat chart can be helpful. It provides a visual reference for understanding how different carat weights typically translate into dimensions across different diamond shapes.

A round brilliant, for example, will have different proportions to an oval or emerald cut, so two diamonds of the same carat weight may not appear the same size when viewed from above.

The charts below offer a useful guide to the relationship between carat weight and millimetre dimensions, helping you get a clearer sense of scale when choosing your diamond.

ROUND DIAMONDS

CARAT WEIGHT	APPROXIMATE MM SIZE
0.25 ct	4 mm
0.50 ct	5 mm
1.00 ct	6.3 mm
1.25 ct	7 mm
1.50 ct	7.3 mm
2.00 ct	8 mm
2.50 ct	8.7 mm
3.00 ct	9.3 mm
3.50 ct	9.7 mm
4.00 ct	10.2 mm
4.50 ct	10.6 mm
5.00 ct	11 mm

OVAL DIAMONDS

CARAT WEIGHT	APPROXIMATE MM SIZE
0.50 ct	6.5 × 4.5 mm
1.00 ct	8 × 5.5 mm
1.25 ct	8.8 × 6 mm
1.50 ct	9 × 6.5 mm
2.00 ct	10 × 7 mm
2.50 ct	11 × 7.5 mm
3.00 ct	11.5 × 8 mm
3.50 ct	12.5 × 8.5 mm
4.00 ct	13 × 9 mm
4.50 ct	13.5 × 7 mm
5.00 ct	14 × 9.5 mm

PEAR DIAMONDS

CARAT WEIGHT	APPROXIMATE MM SIZE
0.50 ct	7 × 4.5 mm
1.00 ct	9 × 5.5 mm
1.25 ct	9.5 × 6 mm
1.50 ct	10 × 6.5 mm
2.00 ct	11 × 7 mm
2.50 ct	12 × 7.5 mm
3.00 ct	13 × 8 mm
3.50 ct	13.5 × 8.5 mm
4.00 ct	14.5 × 9 mm
4.50 ct	15 × 7 mm
5.00 ct	15.5 × 9.5 mm

EMERALD DIAMONDS

CARAT WEIGHT	APPROXIMATE MM SIZE
0.50 ct	5.5 × 4 mm
1.00 ct	7 × 4.5 mm
1.25 ct	7.5 × 5 mm
1.50 ct	8 × 5.5 mm
2.00 ct	8.5 × 6 mm
2.50 ct	9 × 6.5 mm
3.00 ct	9.7 × 7 mm
3.50 ct	10.3 × 7 mm
4.00 ct	10.7 × 7.5 mm
4.50 ct	11 × 6 mm
5.00 ct	11.5 × 8 mm

PRINCESS DIAMONDS

CARAT WEIGHT	APPROXIMATE MM SIZE
0.50 ct	4.4 mm
1.00 ct	5.5 mm
1.25 ct	5.9 mm
1.50 ct	6.3 mm
2.00 ct	7 mm
2.50 ct	7.5 mm
3.00 ct	8 mm
3.50 ct	8.3 mm
4.00 ct	8.7 mm
4.50 ct	9 mm
5.00 ct	9.3 mm

Please note: These measurements are approximate. The dimensions of an individual diamond can vary according to its cut, proportions and depth, so carat weight should not be treated as an exact measurement of visible size.