Gem size glossary: carat, ctw, DEW, melee, face-up and more
By HeyGema™ · Updated
In short
The terms you meet when sizing a stone, in plain words: a carat is 200 milligrams, ctw is the weight of all stones in a piece, DEW is the weight of a diamond of the same size, and face-up is how big the stone looks from above.
- Carat (ct)
- A unit of weight for gemstones: 200 milligrams, or 0.2 grams. It measures weight, not size. Not the same as karat, which measures gold purity.
- Point
- One hundredth of a carat, 2 milligrams. A 50 point diamond weighs half a carat.
- ctw (carat total weight)
- The weight of all the stones in a piece added together. A pair of 1 ctw studs is two stones of about half a carat each.
- Face-up size
- How big a stone looks from above, as length and width in mm or as face-up area. Two stones of the same weight can have different face-up sizes.
- Length-to-width ratio
- The long side of a fancy shape divided by the short side. An oval of 1.45:1 is 45% longer than it is wide.
- DEW (diamond equivalent weight)
- The weight a diamond of the same size would have. Moissanite is usually labeled by DEW so it can be compared with diamond.
- Melee
- Small diamonds, usually under about 0.2 carat or 3 mm across, used as side stones, in pavé and as accents.
- Calibrated size
- A standard stone size in mm that ready-made settings are made for.
- Table
- The flat top face of a faceted stone.
- Crown, pavilion, girdle, culet
- The parts of a faceted stone: the crown is the top above the girdle, the pavilion the bottom, the girdle the thin edge around the widest part, and the culet the point at the bottom.
- Depth
- The height of a stone from the table to the culet, in mm or as a percent of its width.
- Specific gravity (SG)
- A material's density against water. Diamond is 3.52, sapphire about 4.0, emerald about 2.72. It sets how big a stone of a given weight is.
- Brilliant cut and step cut
- A brilliant cut has triangular and kite-shaped facets for sparkle (round, oval, pear). A step cut has long rectangular facets in rows, like stairs (emerald cut, Asscher).
- Cabochon
- A stone with a smooth, domed top and no facets, usual for opal, turquoise and star stones.
- Lab grown diamond
- A diamond made in a lab. It has the same properties as a mined diamond, so it has the same size for a given weight.
Questions
Carat total weight: the combined weight of every stone in a piece of jewelry.
Diamond equivalent weight: the weight a diamond of the same size would have.
Small diamonds, usually under about 0.2 carat or 3 mm across.