Diamond Carat Weight Calculator
Estimate carat weight based on stone dimensions (mm)
Understanding Diamond Carat Estimation
In the world of gemology, estimating the weight of a mounted diamond or verifying a loose stone requires precise measurements of its physical dimensions. While a scale is the most accurate method, the mathematical estimation formula provides a highly reliable approximation based on the specific gravity of carbon crystals (diamond) and the geometry of specific cuts.
How the Calculation Works
This calculator uses industry-standard formulas developed by gemologists to convert millimeters into carats. The basic logic follows the volume of the geometric shape multiplied by the density of a diamond (3.52) and an adjustment factor for the girdle thickness and crown height.
- Round Brilliant: Diameter² × Depth × 0.0061
- Princess Cut: Length × Width × Depth × 0.0083
- Oval: Length × Width × Depth × 0.0062
- Emerald/Baguette: Length × Width × Depth × 0.0080
- Marquise: Length × Width × Depth × 0.0058
- Pear Shape: Length × Width × Depth × 0.00615
Why Accuracy Matters
Even a 0.1mm difference in depth can significantly alter the carat weight. For example, a 6.5mm Round Brilliant diamond with a depth of 4.0mm is approximately 1.04 carats. If the depth is actually 3.8mm, the weight drops to roughly 0.98 carats. This difference is crucial for valuation, as diamonds hitting "magic numbers" (like 1.00ct) often carry a price premium.
Practical Example: Oval Cut
Imagine you have an oval diamond with a length of 8.0mm, a width of 6.0mm, and a depth of 3.7mm. The calculation would be:
Note: These formulas assume a standard "medium" girdle. If the diamond has an extremely thick girdle, the actual weight may be 2-5% higher than the estimate.