Momme
A Japanese unit of weight used in the pearl trade, equal to 3.75 grams. Used wholesale, rarely at retail.
One momme is 3.75 grams, or 18.75 carats. It survives from the Japanese origins of pearl culturing.
Loose pearls and strands are bought by momme at wholesale, so a price per momme is a trade price rather than a shop price.
Retail sells pearls by the piece or by the strand, priced on millimetre size, shape and quality instead.
When you are buying
If a seller quotes you a momme price, you are being quoted wholesale. Ask what the finished piece costs, since stringing, clasp and matching are not in that number.
Carat
A unit of gemstone weight, equal to 0.2 grams. Nothing to do with karat, which measures gold purity.
Pearl Size
The diameter of a pearl in millimetres, measured across its widest point. Price rises steeply, not evenly, with size.
Tola
A traditional South Asian weight, about 11.66 grams. Still used in conversation, rarely on the bill.
Per Gram Pricing
Pricing a piece on what it weighs, at the day's rate for its purity, plus labour. The traditional gold model.