Diamond Weight Estimator
Estimate diamond carat weight from measurements.
Enter length, width, depth, and shape for accurate weight estimation.
Diamond carat weight can be estimated from physical measurements using shape-specific formulas. This is useful when a diamond is already set in jewelry and cannot be weighed directly on a scale.
General Formula:
Carat Weight = Length × Width × Depth × Shape Factor
All measurements are in millimeters (mm). The shape factor accounts for the different volume distributions of each diamond cut.
Shape Factors:
| Diamond Shape | Shape Factor | Formula Notes |
|---|---|---|
| Round Brilliant | 0.0061 | Most common cut; uses average diameter |
| Princess (Square) | 0.0083 | Square shape; L and W are similar |
| Oval | 0.0062 | Elongated shape |
| Emerald | 0.0080 | Rectangular step-cut |
| Pear | 0.0059 | Teardrop shape |
| Marquise | 0.0059 | Boat/eye shape |
| Cushion | 0.0074 | Rounded square |
| Radiant | 0.0081 | Trimmed-corner rectangle |
| Asscher | 0.0080 | Square step-cut |
| Heart | 0.0059 | Heart shape |
Worked Example — Round Diamond: A round diamond measures 6.5 mm diameter × 4.0 mm depth: Weight = 6.5 × 6.5 × 4.0 × 0.0061 = 1.031 carats
Worked Example — Princess Cut: A princess diamond measures 5.5 mm × 5.5 mm × 3.8 mm: Weight = 5.5 × 5.5 × 3.8 × 0.0083 = 0.954 carats
Worked Example — Oval: An oval diamond measures 8.0 mm × 5.5 mm × 3.5 mm: Weight = 8.0 × 5.5 × 3.5 × 0.0062 = 0.955 carats
Typical dimensions by carat weight (Round Brilliant):
| Carats | Diameter (mm) | Depth (mm) |
|---|---|---|
| 0.25 | 4.1 | 2.5 |
| 0.50 | 5.2 | 3.1 |
| 0.75 | 5.8 | 3.5 |
| 1.00 | 6.5 | 3.9 |
| 1.25 | 6.9 | 4.2 |
| 1.50 | 7.4 | 4.5 |
| 2.00 | 8.2 | 5.0 |
| 3.00 | 9.4 | 5.7 |
Important notes:
- These are estimates. Actual weight can vary by 5–10% depending on the exact proportions and cut quality.
- Deeper-cut diamonds will weigh more for the same face-up diameter.
- Poorly proportioned diamonds may appear smaller than their carat weight suggests.
- For accurate carat weight, the diamond should be weighed on a gemological scale (0.01 ct precision).
How to measure a mounted diamond:
- Use a jewelry caliper or millimeter gauge.
- For round diamonds, measure the diameter from two directions and average them.
- Depth can be measured with a leveridge gauge or estimated from the side profile.
- If the diamond is in a bezel setting, only approximate measurements may be possible.
Understanding carats:
- 1 carat = 200 milligrams (0.2 grams)
- The word “carat” comes from the carob seed, which was historically used as a balance weight.
- Carat weight is one of the “4 Cs” of diamond grading (Cut, Color, Clarity, Carat).