The radiant cut diamond is a dazzling hybrid that combines the brilliant sparkle of round cuts with the elegant shape of emerald cuts. Its cropped corners, rectangular or square outline, and 70+ facets make it a favorite for those seeking both fire and durability.
Whether you’re buying an engagement ring, upgrading your jewelry, or simply curious about diamond proportions, understanding millimeter dimensions (mm) versus carat weight is essential. While carat weight tells you how much a diamond weighs, its dimensions tell you how large it will look on the finger - and two radiant cut diamonds of the same carat weight can appear different in size depending on depth and table percentages.
📐 Why Radiant Cut Sizes Can Vary
Radiant cuts have unique proportions that can slightly change their visual spread.
Main factors:
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Depth percentage – A deeper cut may carry more weight without looking larger from the top view.
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Length-to-width ratio (L/W) – Square shapes (1.00 ratio) look different from elongated shapes (1.20–1.35 ratio) even at the same weight.
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Table percentage – Larger tables can create the illusion of a bigger stone.
📊 Radiant Cut Diamond Size Chart
Below is a combined chart showing approximate conversions for both mm to carat and carat to mm.
(Values are averages; actual size will vary depending on cut proportions.)
| MM (Length × Width) | Approx. Carat Weight | Carat Weight | Approx. MM Size |
|---|---|---|---|
| 5.0 × 3.5 mm | 0.50 ct | 0.50 ct | 5.0 × 3.5 mm |
| 6.0 × 4.0 mm | 0.75 ct | 0.75 ct | 6.0 × 4.0 mm |
| 6.5 × 4.5 mm | 1.00 ct | 1.00 ct | 6.5 × 4.5 mm |
| 7.0 × 5.0 mm | 1.25 ct | 1.25 ct | 7.0 × 5.0 mm |
| 7.5 × 5.5 mm | 1.50 ct | 1.50 ct | 7.5 × 5.5 mm |
| 8.0 × 6.0 mm | 2.00 ct | 2.00 ct | 8.0 × 6.0 mm |
| 8.5 × 6.5 mm | 2.50 ct | 2.50 ct | 8.5 × 6.5 mm |
| 9.0 × 7.0 mm | 3.00 ct | 3.00 ct | 9.0 × 7.0 mm |
| 9.5 × 7.5 mm | 3.50 ct | 3.50 ct | 9.5 × 7.5 mm |
| 10.0 × 8.0 mm | 4.00 ct | 4.00 ct | 10.0 × 8.0 mm |
💡 Tips for Choosing the Perfect Radiant Cut Size
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Consider your finger size – Smaller fingers make a diamond look bigger; larger fingers may need more spread for the same visual effect.
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Mind the ratio – Square radiants (L/W ≈ 1.00) appear chunkier, while rectangular radiants (L/W ≈ 1.25) look more elongated.
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Play with settings – A halo setting can make your radiant cut appear up to 1 carat larger without the extra cost.
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Avoid overpaying for “magic sizes” – Stones just below common weight jumps (e.g., 1.90 ct instead of 2.00 ct) can be 10–20% cheaper with minimal visual difference.
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Check depth & table – Ideal depth (61–69%) and table (61–69%) help maximize sparkle and spread.
Understanding the Radiant Cut Diamond Size Chart lets you shop smarter, balance budget with beauty, and choose a diamond that looks perfect on your hand. Whether you prefer a glamorous rectangular shape or a balanced square radiant, knowing the mm-to-carat relationship ensures you get the most sparkle for your money.
