Diamond Size Chart – Carat to MM for All Shapes

Gemological Reference

Diamond Size Chart: Carat to MM for All Diamond Shapes

Accurate carat-to-mm conversions for all 11 diamond shapes — from 0.08 ct to 20 ct. Based on standard gemological proportions.

Round Diamond Size Chart (Carat to MM)

The most popular diamond shape, maximizing brilliance with 57–58 facets. Measurements given as diameter (mm). Ideal depth ratio: 59–62.5%.

58 Facets Symmetric Best Brilliance Ideal L/W Ratio: 1.0

Round diamond carat weight to diameter in millimeters.
Diameter (mm)	Carat Weight	Approx. Depth	Actual Size	Category

How to Measure

Measure the widest diameter across the girdle using calipers. Average two perpendicular readings for irregularly cut stones.

1 Carat Standard

A 1.00 ct round diamond with ideal proportions measures approximately 6.4–6.5 mm in diameter.

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Natural Diamonds Lab-grown Diamonds

Oval Diamond Size Chart (Carat to MM)

Elongated shape that makes fingers appear longer. Two measurements: Length × Width. Ideal L/W ratio: 1.30–1.50.

56–58 Facets Elongated Ideal L/W: 1.35–1.45

Oval diamond carat weight to length and width in millimeters.
Length × Width (mm)	Carat Weight	L/W Ratio	Actual Size	Category

Pear Shape (Teardrop)

Combines round and marquise shapes with a pointed tip. Worn with the point toward the fingers for a slimming effect. Ideal L/W: 1.45–1.75.

58 Facets Teardrop Shape Ideal L/W: 1.50–1.70

Pear-shaped diamond carat weight to length and width in millimeters.
Length × Width (mm)	Carat Weight	L/W Ratio	Actual Size	Category

Marquise Cut (Navette)

Boat-shaped with pointed ends, maximising carat weight appearance. Ideal L/W ratio: 1.75–2.25. Recommended with V-prong protection at tips.

55–58 Facets Boat-Shaped Ideal L/W: 1.85–2.10

Marquise diamond carat weight to length and width in millimeters.
Length × Width (mm)	Carat Weight	L/W Ratio	Actual Size	Category

Emerald Diamond Size Chart (Carat to MM)

Step-cut rectangular shape with cut corners. Showcases clarity over brilliance — inclusions are more visible. Ideal L/W ratio: 1.30–1.50.

50–58 Facets Step Cut Ideal L/W: 1.35–1.50

Emerald-cut diamond carat weight to length and width in millimeters.
Length × Width (mm)	Carat Weight	L/W Ratio	Actual Size	Category

Princess Diamond Size Chart (Carat to MM)

Square shape with pointed corners, the second most popular cut. High brilliance for a square shape. Size given as side length (square).

57–76 Facets Square Ideal L/W: 1.00–1.05

Princess-cut diamond carat weight to side length in millimeters.
Side Length (mm)	Carat Weight	Approx. Depth	Actual Size	Category

Cushion Diamond Size Chart (Carat to MM)

Square or rectangular with rounded corners and large facets that enhance clarity. Available in “classic” and “modified” variants. Ideal L/W: 1.00–1.09.

58–64 Facets Soft Corners Ideal L/W: 1.00–1.05

Cushion-cut diamond carat weight to length and width in millimeters.
Length × Width (mm)	Carat Weight	Approx. Depth	Actual Size	Category

Heart Diamond Size Chart (Carat to MM)

The most romantic diamond shape. Requires skilled cutting for symmetry. Size given as width. Ideal L/W ratio: 0.90–1.10 (near 1:1).

56–58 Facets Romantic Ideal L/W: 0.95–1.05

Heart-shaped diamond carat weight to width in millimeters.
Width (mm)	Carat Weight	Approx. Height	Actual Size	Category

Radiant Diamond Size Chart (Carat to MM)

A rectangular brilliant-cut with cropped corners — combines the fire of a round with the elegance of an emerald outline. More popular than the square version. Ideal L/W: 1.25–1.50.

62–70 Facets Brilliant Facets Ideal L/W: 1.25–1.50

Radiant-cut diamond carat weight to length and width in millimeters.
Length × Width (mm)	Carat Weight	L/W Ratio	Actual Size	Category

Asscher Diamond Size Chart (Carat to MM)

A square step-cut with deeply cropped corners resembling an octagon. Created in 1902. Distinctive “hall of mirrors” effect. Nearly square L/W: 1.00–1.05.

58 Facets Step Cut Vintage Style Ideal L/W: 1.00–1.05

Asscher-cut diamond carat weight to side length in millimeters.
Side Length (mm)	Carat Weight	Approx. Depth	Actual Size	Category

Trillion Cut (Trilliant)

Triangular shape with three equal sides. Used as solitaire or flanking side stones. Measurement is the width across the widest point (side length).

31–50 Facets Triangular Equilateral

Trillion-cut diamond carat weight to side length in millimeters.
Side Length (mm)	Carat Weight	Approx. Depth	Actual Size	Category