When choosing a cushion cut diamond, one of the most common questions is: "How big will it look?" While carat weight measures the stone’s mass, the millimeter (mm) dimensions show how much space it actually covers on your finger. Because cushion cuts have rounded corners and varying depth percentages, two diamonds of the same carat weight can look slightly different in size.
In this guide, you’ll find an easy-to-read cushion cut diamond size chart to convert mm to carat and carat to mm, plus tips for selecting the perfect size.
Understanding Cushion Cut Diamond Proportions
The cushion cut combines the square or rectangular shape of an emerald or princess cut with soft, rounded edges, resembling a pillow (hence the name). Its brilliance comes from a mix of brilliant-cut and step-cut facets, creating a romantic, vintage-inspired sparkle.
Two key factors influence how large your cushion cut diamond appears:
-
Length-to-width ratio – Square cushions (1.00–1.05 ratio) look more classic, while elongated cushions (1.10–1.20+) create a slender, elegant feel.
-
Depth percentage – Shallower stones face up larger for their carat weight, while deeper ones appear smaller.
📊 Cushion Cut Diamond Size Chart
| MM (Length × Width) | Approx. Carat Weight | Carat Weight | Approx. MM Size |
|---|---|---|---|
| 4.5 × 4.5 mm | 0.50 ct | 0.50 ct | 4.5 mm |
| 5.0 × 5.0 mm | 0.75 ct | 0.75 ct | 5.0 mm |
| 5.5 × 5.5 mm | 1.00 ct | 1.00 ct | 5.5 mm |
| 6.0 × 6.0 mm | 1.25 ct | 1.25 ct | 6.0 mm |
| 6.5 × 6.5 mm | 1.50 ct | 1.50 ct | 6.5 mm |
| 7.0 × 7.0 mm | 2.00 ct | 2.00 ct | 7.0 mm |
| 7.5 × 7.5 mm | 2.50 ct | 2.50 ct | 7.5 mm |
| 8.0 × 8.0 mm | 3.00 ct | 3.00 ct | 8.0 mm |
| 8.5 × 8.5 mm | 3.50 ct | 3.50 ct | 8.5 mm |
| 9.0 × 9.0 mm | 4.00 ct | 4.00 ct | 9.0 mm |
