Carat weight and millimetres: how to compare loose gemstones

When comparing loose gemstones, carat weight and size answer different questions. Carats describe mass; millimetres describe the dimensions a jeweller must work with. Looking at both makes it easier to choose a stone for an existing setting or a new design.

What does one carat mean?

One metric carat is 0.2 grams. The number does not specify diameter, length or depth. Proportions and the gemstone material influence how much of that weight is visible from above. Even within one gemstone type and one cut, two stones can share a carat weight without having identical measurements.

Compare two oval white topazes at 1.10 ct

Our 1.10 ct oval white topaz measuring 6.97 × 5.10 × 3.77 mm and 1.10 ct oval white topaz measuring 7.03 × 5.01 × 3.47 mm have the same listed weight but different dimensions. The first is slightly wider and deeper; the second is slightly longer. Neither set of measurements alone establishes which stone has the better appearance. They show why the setting must be planned around the selected stone.

For round stones, read diameter and depth

A round listing may show two dimensions because a circle is described by its diameter. The 5.95 mm round white topaz has a depth of 4.21 mm. Keep those roles separate when discussing the stone with your jeweller. Depth affects the space beneath the visible face and cannot be inferred from diameter alone.

A short comparison method

First choose the required outline. Then compare length and width, or diameter for a round stone. Check depth next, and use carat weight as an additional specification. Confirm the quantity and price shown for that individual listing. Do not treat equal carat weights as a ready-made pair or assume a nominal setting size guarantees a fit.

Browse white topaz with individual measurements, read about choosing stones for earrings, or send MANĒKO your required dimensions.