The momme, unit of mass
The momme weighs exactly 3.75 grams, a thousandth of the kan. It is the smallest of the Japanese mass units still in everyday commercial use.
It left Japan with the cultured pearl: Kokichi Mikimoto patented his method in 1896, and the wholesale pearl trade has quoted prices per momme ever since, in Kobe as in Hong Kong. Beware the other momme: the number printed on a bolt of silk, 19 momme charmeuse for instance, is a weight per unit area and not a mass, and it does not convert with this factor.
The momme in other units
| 1 momme | 0.00000375 t |
| 1 momme | 0.00375 kg |
| 1 momme | 3.75 g |
| 1 momme | 3,750 mg |
| 1 momme | 0.00826733 lb |
| 1 momme | 0.132277 oz |
| 1 momme | 0.120565 oz t |
| 1 momme | 0.000590524 st |
| 1 momme | 18.75 ct |
| 1 momme | 0.00000413367 ton US |
| 1 momme | 0.00000369077 ton UK |
| 1 momme | 3,750,000 µg |
| 1 momme | 0.0075 lb metric |
| 1 momme | 0.321507 tola |
| 1 momme | 0.001 kan |
Frequently asked questions
How many carats is a momme?
Exactly 18.75 carats, and 75 pearl grains, the grain being a quarter of a carat. Wholesalers weigh lots in momme, retail describes the single pearl in carats or grains, and all three scales meet without any rounding at all.
Was the momme ever money?
It was the unit of account for silver, which Edo Japan circulated by weight rather than by coin. The shogunal order of 1609 set one ryō of gold at fifty momme of silver, revised to sixty in 1700. Osaka wrote its prices in momme while Edo wrote them in ryō.
Is the Chinese mace the same as a momme?
In Taiwan yes: the tael was aligned on 37.5 grams during the Japanese period, so its tenth weighs the same as the momme. In Hong Kong no: the tael there follows the avoirdupois ounce, one and a third exactly, which gives 37.7994 grams and a mace of 3.77994 grams, eight tenths of a per cent heavier.