Diamond Carat Calculator

A diamond carat is a unit of mass equal to 200 milligrams. Jewelers normally determine carat weight with a calibrated scale, but dimensions provide a useful estimate when a stone cannot be removed from its setting or when reviewing a grading description. This calculator is designed for round brilliant diamonds and combines average diameter, total depth, and an empirical diamond-density coefficient to estimate weight. The formula multiplies diameter by diameter, then by depth, and then by 0.0061. Diameter and depth must both be measured in millimeters. For a stone that is not perfectly circular, measure the minimum and maximum girdle diameter and enter their average. The coefficient reflects the typical outline and pavilion profile of a modern round brilliant, as well as diamond's density. Because real stones vary in girdle thickness, crown height, pavilion depth, and culet size, dimensional weight remains an approximation. Depth percentage is also reported by dividing total depth by average diameter and multiplying by 100. It helps describe how a diamond's vertical proportions compare with its face-up spread. Two stones can weigh the same but look different in diameter because one carries more mass in a deep pavilion or thick girdle. A deeper stone may face up smaller, while an unusually shallow stone may spread wider but can have compromised light performance. Use a millimeter gauge or digital caliper that is suitable for gems. Avoid squeezing the stone, and do not let metal jaws scratch a setting. Measurements from photographs are unreliable unless the image contains a precise scale in the same plane as the diamond. Mounted stones can be especially difficult to measure because prongs obscure the girdle and prevent direct access to the total depth. The estimate is useful for inventory checks, insurance preparation, buying comparisons, and educational exercises, but it does not replace a laboratory grading report or an actual scale measurement. Small dimensional errors are amplified because diameter is squared. A difference of only a few hundredths of a millimeter can shift the displayed result, particularly for larger stones. Treat the answer as a reasonable range and consult a qualified gemologist when value, identity, or exact weight matters.