What Is the Diamond Weight Calculator?
This calculator estimates the weight of a round brilliant cut diamond in carats based on its physical measurements: the average diameter and the depth, both in millimeters. It is a handy tool for jewelers, appraisers, and buyers who want to estimate carat weight without removing a stone from its setting, where a scale cannot be used.
How to Use It
Measure the average girdle diameter of the round diamond in millimeters (average the maximum and minimum if the stone is slightly out of round). Then measure the depth from the table down to the culet. Enter both values and the calculator returns the estimated carat weight.
The Formula Explained
For a round brilliant diamond the standard estimation formula is:
$$\text{Carat} = \text{Diameter (mm)}^{2} \times \text{Depth (mm)} \times 0.0061$$
The factor 0.0061 combines the density of diamond with the geometric volume of a typical round brilliant. For stones with thick girdles or unusual proportions, a slightly higher factor (e.g. 0.0066) is sometimes used to improve accuracy.
Worked Example
Suppose a round diamond measures 6.5 mm in diameter and 4.0 mm in depth. The weight is $$6.5^{2} \times 4.0 \times 0.0061 = 42.25 \times 4.0 \times 0.0061 = 169 \times 0.0061 \approx 1.0309 \text{ carats}$$ — close to a 1-carat stone, which is typically about 6.5 mm wide.
FAQ
Is this exact? No — it is an estimate. Actual weight depends on the cut, girdle thickness, and culet. Use a scale for an exact carat weight when possible.
Does it work for fancy shapes? This formula is specific to round brilliant diamonds. Ovals, princess, and other shapes use different formulas and correction factors.
What is a typical 1-carat diameter? A well-cut 1-carat round brilliant is usually about 6.4–6.5 mm in diameter.
