Per Momme — The Japanese Weight Standard for Akoya Pearl Pricing
Per Momme — The Japanese Weight Standard for Akoya Pearl Pricing
A pricing convention based on the 3.75-gram momme, the legacy unit of the Japanese pearl industry that survives in international wholesale trade
Per momme is the traditional Japanese pricing convention for Akoya cultured pearls, in which price is quoted per momme — a unit equal to 3.75 grams or 18.75 carats. The momme is one of the surviving units of the historical Japanese kan-in weight system, retained in the pearl industry because the Akoya trade developed in Japan during the period when the country's commercial weights and measures were in transition between the traditional system and the international metric standard. By international convention the momme is now defined as exactly 3.75 grams, and per-momme pricing remains the standard for Japanese-source Akoya pearl strands and keshi.
How it works
A dealer offering an Akoya strand at $200 per momme, with a strand weight of 4.2 momme (15.75 grams), is asking $840 for the strand. The convention is identical in form to per-carat pricing for faceted gemstones, with the momme standing in for the carat as the relevant unit. The total price for any lot is the per-momme rate multiplied by the lot's weight in momme, with most dealers quoting weights to one or two decimal places.
Wholesale Akoya transactions in Japan, in the Hong Kong Jewellery & Gem Fair, and in the international markets that source from Japanese producers continue to use the per-momme convention as a matter of trade tradition. The unit is sufficiently familiar in the international Akoya trade that buyers from non-momme markets readily learn to work with it, in the same way that diamond buyers internationally work with carats regardless of their home unit system.
Why momme rather than gram
The per-momme convention is partly inertia and partly utility. The momme survived as a pearl industry standard because the early-twentieth-century cultured-pearl industry built its grading frameworks, its inventory systems, and its trade language around the unit, and changing it would require renegotiating decades of pricing references. The unit also has the practical convenience of producing whole-number price quotations for typical Akoya strand weights — a 1.5-momme strand and a 2-momme strand are intuitive sizes for the trade in a way that 5.625-gram and 7.5-gram strands are not.
In the trade
Per-momme pricing is essentially universal for Japanese Akoya at wholesale level. Per-strand and per-pearl pricing dominate at retail, with the dealer having converted from momme into the convention used by the destination market. Buyers approaching Japanese dealers, attending the Tokyo or Kobe pearl auctions, or shopping in the Hong Kong fairs should expect per-momme quotations and should arrive with a working sense of the momme-to-gram conversion. The standard pearl-grading framework — bodycolour, overtone, lustre, surface, shape, size — applies to per-momme transactions as it does to all Akoya pricing.