The Standard Formula
for calculating the mass (volume actually) of gemstone cuts has been
known for some time, and produces reasonable results in many cases.
More sophisticated estimates are available for certain
cuts, in which the effects of belly shape, culet size, girdle size, etc.,
can be adjusted for. We call this our "Advanced Formula", and the
results are available in our Carat Weight Estimation page.
The parameters were carefully optimized using data on over 1,000
individual characterized gemstones. By performing
multi-dimensional curve fits to the data, it was possible to separate out
the effects on volume of a whole variety of different shape factors.
For example, cutting a larger culet might not seem to have
any significant effect on the mass of a stone, but if you think about it,
what it means is that the depth measurement, which is taken from the
culet to the table, will be different from what you would otherwise get
on the same stone with a smaller culet. The Depth will read
smaller. Using the Standard Formula's
basic Length*Width*Depth metric, this will result in a significantly
lighter estimate of the stone. Our formula corrects for this
effect, so the culet size entry in effect modifies the Depth measurement
you have specified. Similar changes happen for the other shape
In addition, testing this formula on such a large set of
characterized stones has given us the data to be able to grade our own
results, so you will see not only a Best Estimate of the weight, but a
tolerance on this number, which takes into account the known error level
we experienced on the stones used in compiling the data, as well as the
tolerances reported to us from the field in specific gravity (or density)
figures for the gemstone species you have selected. Thus, you will
find better results for Diamonds than for Quartz, as Quartz has such a
wide range of specific gravity. This improvement will show up in
the tolerance reading we report.
Accuracy / User Beware!
This Formula has proven accurate in our tests. It is
possible, however, that there is a misteak in our data or
estimation algorithm or that your stone may lie outside the size range of
our tests. Always use common sense in evaluating the results of
computer calculations. Computers are amazingly fast, very obedient,
and incredibly useful tools. But they are dumbbeyond
comprehension. Our server will happily estimate a weight for
your stone, but it only knows what it has been told. It has never
seen a gemstone, and has no common sense about what is reasonable or
absurd. Please inform us of problems.
Naturally, we take no
responsibility for your use or misuse of this data.