This is perhaps one of the most common misconceptions in the diamond world.
Put simply, just because 2 diamonds weight the same, it doesn’t mean they have the same physical dimensions.
Put two one carat round diamonds side by side, and their physical dimensions are likely to be different. Yes, marginally different, but different nonetheless.
This is because one carat refers to the WEIGHT of the diamond, and what determines the weight of something? Yes, think back to elementary school math…..the length, width and depth.
A typical one carat round diamond SHOULD (if we’re aiming for the ideal scenario here) measure approx 6.5mm in diameter. If diamond A measures only 6.3mm in diameter and the diamond B measures 6.7mm in diameter, then diamond A is quite deep – that is to say that an overly large % of the diamond is in the depth of the stone. Vice versa, diamond B has a large table which, on the face of it, might sound good as diamond B LOOKS larger than a one carat. However, it is not at the optimum depth for sparkle…in other words it is too shallow. A diamond which is too deep or too shallow will not refract light to its maximum and so the sparkle factor could be compromised.
This is exactly the reason why there are quite strict parameters for determining the quality of, especially, round brilliant cut diamonds. Not only are the well-versed “4Cs” important, but also the way in which the diamond is cut and prorportioned.