Pearl Weight (Momme) Calculator
Convert between momme, grams, carats, and pearl grains, or estimate a round pearl’s weight from its diameter.
Weight in momme
1 momme = 3.75 g; 1 carat = 0.2 g; 1 pearl grain = 0.05 g. The diameter mode is an estimate for round pearls and does not account for baroque shapes or nacre variation.
The unit the pearl trade runs on
Long before pearls were sold by the strand in shops, they were weighed by the momme in Japan’s pearling houses, and the unit stuck. A momme is 3.75 grams, and wholesale Akoya lots are still quoted that way. Carats and pearl grains carry over from the wider gem trade — a grain is a quarter of a carat — so the same parcel can be described several ways.
The diameter estimate is handy when you have pearls but no scale: model each as a small sphere of nacre and you get a weight close enough to sanity-check a quote or an invoice.
Frequently Asked Questions
What is a momme?
The momme (匁) is the traditional Japanese unit pearls have long been weighed and traded in. One momme equals 3.75 grams. Loose pearls and strands, especially Akoya, are still quoted in momme in the wholesale trade.
How do momme, carats, and grains relate?
1 momme = 3.75g, 1 carat = 0.2g, and 1 pearl grain = 0.05g (a quarter of a carat). So one momme is 18.75 carats or 75 pearl grains. The tool shows all of them at once.
Can I estimate weight from pearl size?
Yes. Switch to diameter mode and the tool treats each pearl as a sphere, working out its volume from the diameter and multiplying by a typical nacre density of about 2.73 g/cm³. It's an estimate for round pearls and won't be exact for baroque shapes or thin-nacre pearls.
Why weigh pearls at all?
Weight is how loose pearls are priced in the trade and how a parcel is checked against an invoice. Converting to momme lets you compare a seller's quote to trade norms, and estimating from size helps sanity-check a strand before it's weighed.