Convert Momme to grams

An exact figure with an odd origin

The momme is one-thousandth of a kan, and the kan was fixed at exactly 3.75 kilograms when Japan tied its traditional units to the metric system. That makes the momme exactly 3.75 g — a clean number that helped it survive metrication in trades where the traditional grading scales were already built around it.

One hundred sixty momme make a kin (600 g), the traditional Japanese pound still seen in tea and bread contexts. The whole shakkanhō system was withdrawn from legal commercial use in the 1950s and 60s, yet the momme persists internationally in exactly two niches.

Pearls: the unit of the trade

Wholesale pearl lots are weighed in momme, and the convention is global — Kobe, Hong Kong, Basel and Tucson all quote it. It survives because the Japanese cultured-pearl industry defined the modern market, and because pearl grading combines size, lustre and nacre with weight in a scale traders learned in momme.

Loose pearls are also quoted in grains and carats, and the three do not interconvert intuitively: one momme is 18.75 metric carats. Any quotation comparing lots priced in different units has to normalise, and mixing carat and momme prices is a recurring source of dispute in secondary-market sales.

Silk: momme as fabric weight

In textiles, momme means something different: it is a measure of areal density, defined as the weight in pounds of a piece of silk 100 yards long and 45 inches wide. A 19-momme charmeuse and a 22-momme charmeuse differ in how much silk is in the cloth, not in how much a bolt weighs.

The practical conversion is that one momme of silk weight is about 4.34 grams per square metre, so 22 momme is roughly 95 g/m². Buyers comparing Chinese mills quoting g/m² with Japanese or American vendors quoting momme need that bridge, and it is the number most silk listings omit.

Using momme figures

For pearls, treat 3.75 g as exact and convert once at the end of a calculation. For silk, never apply the pearl figure: the textile momme is a density, and 3.75 g has no meaning there. The same word measuring two different quantities in two adjacent luxury trades is the main hazard this unit presents.

Insurance schedules and customs declarations increasingly demand metric mass for pearls, so record both the momme figure from the trade document and the gram equivalent, exactly as with the tola in bullion.

Pearls, silk and the surviving trades

The momme of 3.75 grams survives in two international trades. Cultured pearls are graded and priced by momme worldwide, a convention inherited directly from the Japanese pearl industry, and silk fabric weight is quoted in momme per unit area, where higher momme means a denser, heavier cloth.

In the silk trade the number functions as a grade rather than a measurement most buyers ever verify: 19 momme is a standard bedding weight, 22 momme a premium one. Converting those figures to grams per square metre is possible but rarely useful, because the market compares momme to momme. In the pearl trade the momme is a genuine mass and converting it to grams is routine for customs and insurance documentation.

Common mistakes to avoid

• Silk momme is an areal density (about 4.34 g/m² per momme), not the 3.75 g pearl weight — the two are unrelated.
• One momme is 18.75 metric carats; comparing carat-priced and momme-priced pearl lots without converting misprices the lot.
• The shakkanhō units are no longer legal for general Japanese commerce; momme survives by trade convention, not by statute.

Questions people ask about the Momme

How many grams is one momme?

Exactly 3.75 g, since the kan was fixed at 3.75 kg and a momme is one-thousandth of a kan.

What does momme mean for silk?

It is a fabric weight: the pounds per 100 yards of 45-inch-wide silk. Roughly 4.34 g/m² per momme, so 19 momme is about 82 g/m² and 22 momme about 95 g/m².

Why are pearls still sold in momme?

Because Japan built the modern cultured-pearl market and the grading and pricing conventions were set in momme. The unit stayed even as Japan itself metricated.