Carat is weight, not size, but what you see on the hand is millimeters. This chart converts every shape and carat weight in the BVDIY ring studio, from 0.50 to 4.00 carats, into approximate face-up dimensions so you can compare options before you choose.
A well-cut 1 carat round lab-grown diamond is about 6.4 mm across, a 2 carat about 8.1 mm, and a 3 carat about 9.3 mm. Size grows more slowly than carat weight: doubling the carat adds only about a quarter to the diameter. Elongated shapes look larger face-up. All figures are approximate and vary with cut proportions.
What does a lab grown diamond carat size chart look like?
The table shows approximate face-up dimensions for the ten shapes and the carat range offered in the ring studio. Round, princess, Asscher, and heart are given as a single width; the other shapes as length × width. Lab-grown and mined diamonds have the same density, so the chart applies to both.
| Carat | Round | Oval | Princess | Cushion | Emerald | Pear | Radiant | Asscher | Marquise | Heart |
|---|---|---|---|---|---|---|---|---|---|---|
| 0.50 ct | 5.1 mm | 6.3 × 4.5 mm | 4.4 mm | 4.8 × 4.4 mm | 5.5 × 3.9 mm | 6.9 × 4.4 mm | 5.2 × 4.2 mm | 4.6 mm | 8.3 × 4.2 mm | 5.2 mm |
| 0.75 ct | 5.8 mm | 7.2 × 5.2 mm | 5.0 mm | 5.5 × 5.0 mm | 6.3 × 4.5 mm | 7.9 × 5.1 mm | 6.0 × 4.8 mm | 5.3 mm | 9.5 × 4.8 mm | 6.0 mm |
| 1.00 ct | 6.4 mm | 7.9 × 5.7 mm | 5.5 mm | 6.1 × 5.5 mm | 6.9 × 4.9 mm | 8.6 × 5.6 mm | 6.6 × 5.3 mm | 5.8 mm | 10.5 × 5.2 mm | 6.6 mm |
| 1.50 ct | 7.4 mm | 9.1 × 6.5 mm | 6.3 mm | 7.0 × 6.3 mm | 7.9 × 5.7 mm | 9.9 × 6.4 mm | 7.6 × 6.0 mm | 6.6 mm | 12.0 × 6.0 mm | 7.5 mm |
| 2.00 ct | 8.1 mm | 10.0 × 7.2 mm | 7.0 mm | 7.7 × 7.0 mm | 8.7 × 6.2 mm | 10.9 × 7.0 mm | 8.3 × 6.6 mm | 7.3 mm | 13.2 × 6.6 mm | 8.3 mm |
| 2.50 ct | 8.7 mm | 10.8 × 7.7 mm | 7.5 mm | 8.3 × 7.5 mm | 9.4 × 6.7 mm | 11.7 × 7.6 mm | 9.0 × 7.2 mm | 7.9 mm | 14.2 × 7.1 mm | 8.9 mm |
| 3.00 ct | 9.3 mm | 11.5 × 8.2 mm | 8.0 mm | 8.8 × 8.0 mm | 10.0 × 7.1 mm | 12.5 × 8.0 mm | 9.5 × 7.6 mm | 8.4 mm | 15.1 × 7.6 mm | 9.5 mm |
| 4.00 ct | 10.2 mm | 12.6 × 9.0 mm | 8.8 mm | 9.7 × 8.8 mm | 11.0 × 7.8 mm | 13.7 × 8.9 mm | 10.5 × 8.4 mm | 9.2 mm | 16.6 × 8.3 mm | 10.4 mm |
Approximate values, calculated from standard diamond weight-estimation formulas with typical proportions (listed below). Real stones of the same carat weight can differ by a few tenths of a millimeter. The grading report of your actual diamond gives its exact measurements.
Why does doubling the carat not double the size?
Carat measures weight, and weight follows volume. A diamond grows in three directions at once, so twice the weight spreads across width, length, and depth. For a round diamond, going from 1 to 2 carats increases the diameter by only about a quarter (from about 6.4 to about 8.1 mm), even though the face-up area grows by around 60%. That is why the step from 0.90 to 1.00 carat, or 1.40 to 1.50, is barely visible while the price jump can be noticeable.
Which diamond shape looks biggest for its carat weight?
Shapes that are long and relatively shallow spread their weight over more surface. Marquise, oval, and pear usually look largest face-up for the same carat. Princess and Asscher cuts are deeper, holding more of their weight below the girdle where you cannot see it, so they tend to look smaller than a round of equal weight. Cushion and radiant sit in between and depend heavily on the individual stone's proportions. A halo setting also makes the center look bigger; see solitaire vs halo.
Why do two diamonds of the same carat measure differently?
Cut proportions. A stone cut too deep hides weight in the pavilion and looks small for its carat; a stone cut too shallow looks large but can leak light and look glassy. Girdle thickness and the length-to-width ratio of fancy shapes also change the outline. That is why choosing a good cut matters more than chasing a number; our guide to choosing a lab-grown engagement ring explains how cut, color, and clarity trade off. You can choose the grading lab when you order, and every center diamond ships with its grading report, which lists the exact measurements.
When is a size chart not enough?
A chart cannot tell you how a stone looks on a particular hand. Finger width changes perception: the same 1 carat looks larger on a slim finger than on a wide one, and a thick band makes a center stone look smaller. It also cannot judge sparkle, which depends on cut quality. Use the chart to narrow the range, then compare options in 3D in the ring studio before deciding.
Proportions used for this chart
- Round: length-to-width 1.00:1, depth 62% of width.
- Oval: length-to-width 1.40:1, depth 62% of width.
- Princess: length-to-width 1.00:1, depth 72% of width.
- Cushion: length-to-width 1.10:1, depth 66% of width.
- Emerald: length-to-width 1.40:1, depth 66% of width.
- Pear: length-to-width 1.55:1, depth 62% of width.
- Radiant: length-to-width 1.25:1, depth 66% of width.
- Asscher: length-to-width 1.00:1, depth 64% of width.
- Marquise: length-to-width 2.00:1, depth 60% of width.
- Heart: length-to-width 1.00:1, depth 60% of width.
Sources: Gemological Center (GCAL), "Diamond Carat Weight Estimation Formulas" in Instructional Diamond Grading, gcalusa.com/instructional-diamond-grading.html (shape factors for princess, Asscher, cushion, heart, marquise, pear, oval, emerald, and radiant); round brilliant formula average diameter² × depth × 0.0061, checked against the GIA sample report figures of 6.41–6.43 × 3.97 mm for 1.00 ct, as worked in Haywoods Gems, "Diamond Weight Estimation Calculator" (haywoodsgems.com/diamonds/weight-estimation-calculator/); Octonus, "Weight-estimation formulas" (3dbook.octonus.com/dataeng/crypted/6_01.htm). Accessed 2026-10-17. Dimensions above are derived from these formulas and are approximate.