1.00 ct Round Benchmark
An ideal-cut 1.00 ct Round Brilliant diamond measures 6.40–6.50 mm in diameter with a 61.5% depth (~3.98 mm) and ~33.2 mm² of face-up surface footprint.
GEMOLOGICAL MILLIMETER & FACE-UP SPREAD REFERENCE
Diamond Carat Size Chart in Millimeters (0.25 ct to 5.00 ct)
Carat (ct) measures physical mass (1.00 ct = 200 milligrams)—not visual size. Because elongated shapes like Oval, Pear, and Marquise distribute more weight across their crown table and less in a deep pavilion, a 1.50 ct Oval appears noticeably larger on the finger than a 1.50 ct Cushion or Asscher cut.
The Cube-Root Visual Law
Doubling carat weight from 1.00 ct to 2.00 ct increases linear diameter by the cube root of 2 ($\sqrt[3]2 \approx 1.26$)—meaning a 2.00 ct Round is 8.10 mm wide (+25% wider, not twice as wide).
Elongated Shape Advantage
Oval (1.35–1.40 L:W ratio) and Pear (1.50 L:W ratio) cuts deliver 12%–18% greater length along the finger phalanx than Round or Cushion cuts of identical carat weight.
1. Master Millimeter Dimensions by Carat Weight & Cut Shape
Every measurement below is computed from ideal-cut GIA proportion standards. Click any carat row to visualize that stone at 1:1 physical scale on your finger in our Diamond Carat Studio:
| Carat Weight | Round Brilliant (mm) | Oval Cut (L × W mm) | Emerald Cut (L × W mm) | Cushion Cut (mm) | Pear Cut (L × W mm) | Princess Cut (mm) |
|---|---|---|---|---|---|---|
| 0.25 ct → | 4.09 mm (13.2 mm²) | 4.85 × 3.59 mm | 4.41 × 3.15 mm | 3.78 × 3.78 mm | 5.42 × 3.53 mm | 3.46 × 3.46 mm |
| 0.50 ct → | 5.16 mm (20.9 mm²) | 6.11 × 4.52 mm | 5.56 × 3.97 mm | 4.76 × 4.76 mm | 6.83 × 4.44 mm | 4.37 × 4.37 mm |
| 0.75 ct → | 5.91 mm (27.4 mm²) | 7.00 × 5.18 mm | 6.36 × 4.54 mm | 5.45 × 5.45 mm | 7.81 × 5.09 mm | 5.00 × 5.00 mm |
| 1.00 ct → | 6.50 mm (33.2 mm²) | 7.70 × 5.70 mm | 7.00 × 5.00 mm | 6.00 × 6.00 mm | 8.60 × 5.60 mm | 5.50 × 5.50 mm |
| 1.25 ct → | 7.00 mm (38.5 mm²) | 8.29 × 6.14 mm | 7.54 × 5.39 mm | 6.46 × 6.46 mm | 9.26 × 6.03 mm | 5.92 × 5.92 mm |
| 1.50 ct → | 7.44 mm (43.5 mm²) | 8.81 × 6.52 mm | 8.01 × 5.72 mm | 6.87 × 6.87 mm | 9.84 × 6.41 mm | 6.30 × 6.30 mm |
| 1.75 ct → | 7.83 mm (48.2 mm²) | 9.28 × 6.87 mm | 8.44 × 6.03 mm | 7.23 × 7.23 mm | 10.36 × 6.75 mm | 6.63 × 6.63 mm |
| 2.00 ct → | 8.19 mm (52.7 mm²) | 9.70 × 7.18 mm | 8.82 × 6.30 mm | 7.56 × 7.56 mm | 10.84 × 7.06 mm | 6.93 × 6.93 mm |
| 2.50 ct → | 8.82 mm (61.1 mm²) | 10.45 × 7.74 mm | 9.50 × 6.79 mm | 8.14 × 8.14 mm | 11.67 × 7.60 mm | 7.46 × 7.46 mm |
| 3.00 ct → | 9.37 mm (69.0 mm²) | 11.11 × 8.22 mm | 10.10 × 7.21 mm | 8.65 × 8.65 mm | 12.40 × 8.08 mm | 7.93 × 7.93 mm |
| 4.00 ct → | 10.32 mm (83.6 mm²) | 12.22 × 9.05 mm | 11.11 × 7.94 mm | 9.52 × 9.52 mm | 13.65 × 8.89 mm | 8.73 × 8.73 mm |
| 5.00 ct → | 11.11 mm (97.0 mm²) | 13.17 × 9.75 mm | 11.97 × 8.55 mm | 10.26 × 10.26 mm | 14.71 × 9.58 mm | 9.40 × 9.40 mm |
2. How Finger Size Changes Perceived Diamond Size
A 1.50 ct Round Brilliant (7.35 mm) covers 48.6% of a petite US size 4.5 finger (15.1 mm wide), creating dramatic, high-impact finger coverage. On a US size 8 finger (18.2 mm wide), that same 7.35 mm diamond covers 40.4% of the finger width—requiring roughly a 2.10 ct stone (8.25 mm) to achieve the exact same visual proportion. Use our interactive Diamond Carat Visualizer to pair your exact ring size with any carat weight and setting style (Solitaire, Pavé Halo, or Three-Stone).