Per-Carat Price — The Standard Pricing Convention of the Gemstone Trade
Per-Carat Price — The Standard Pricing Convention of the Gemstone Trade
The dollars-per-carat figure on which gemstone wholesale and retail pricing is built, and the non-linear scaling that makes it more than a unit conversion
Per-carat price is the central pricing convention of the international gemstone trade. A stone is quoted at a price per carat, the buyer multiplies that figure by the stone's actual carat weight, and the result is the total transaction price. The convention is simple in arithmetic and consequential in practice, because per-carat prices do not scale linearly with size, and a stone twice as heavy as another can command four, five, or ten times the per-carat figure depending on species and quality.
How it works
A jeweller offering a 1.50-carat blue sapphire at $4,000 per carat is asking $6,000 for the stone. The same dealer offering a 3.00-carat sapphire of the same colour and clarity might price it at $8,000 per carat, for a total of $24,000 — four times the price of the smaller stone, despite only twice the weight. The difference is rarity: clean, well-coloured rough at three carats is far less common than at one and a half carats, and the per-carat price reflects the difficulty of finding the larger stone.
The non-linear scaling of per-carat prices with size is the single most important fact in coloured-stone pricing, and it is the reason published price guides — Rapaport for diamonds, GemGuide for coloured stones, the Gem Market News for trade-grade material — organise their tables in size brackets. A diamond moves from one Rapaport price band to the next as its weight crosses a magic-number threshold (0.50, 1.00, 1.50, 2.00 carats and so on), and the per-carat price can jump ten or twenty percent at the threshold even though the stone's other characteristics are unchanged.
Why per-carat rather than per-stone
The per-carat convention allows direct comparison of stones of different sizes within the same quality bracket. A buyer evaluating two 0.95-carat and 1.15-carat diamonds of similar quality can compare per-carat prices and understand immediately whether the dealer is treating the two stones consistently. Per-stone pricing would require the buyer to do the arithmetic in their head before any comparison was possible. The convention also allows clean expression of premium or discount levels in trade communication: a 10 percent premium on a published price is well-understood shorthand, where it would be ambiguous in per-stone terms.
Variants and exceptions
Per-carat pricing dominates faceted-stone wholesale and retail. Other conventions apply in specific contexts. Pearls are quoted per gram (most freshwater commercial production), per momme (Akoya tradition), or per pearl (premium South Sea, Tahitian, and unique baroques). Rough is sometimes quoted per kilogram or per parcel rather than per carat. Bead and cabochon production for the costume and beadwork market is quoted per strand or per piece. Within the faceted-stone market, however, per-carat is the universal default.
In the trade
A buyer working with a coloured-stone dealer should ask first for the per-carat price, then confirm the stone's exact weight, and then verify the multiplication. Honest dealers price consistently across their inventory; a stone offered at a per-carat figure substantially below the published price guide range is either a bargain or a problem, and the buyer's first task is to determine which. For diamonds, the Rapaport sheet is the universal reference; for coloured stones, GemGuide and direct comparison with similar offers from other dealers are the available tools.