Monme: A Guide to Reading Japanese Sword Weight in Traditional Units

What is Monme? — A Traditional Unit of Weight

When discussing the dimensions of nihontō, the length units "shaku, sun, and bu" covered in nagasa classification are well known. However, there is another traditional unit used in the world of swords to express weight: monme. In old sword catalogs, box inscriptions, and antique market records, the weight of blades and tōsōgu is sometimes recorded in monme. Without being able to read this unit, it is impossible to accurately understand the information in such old documents.

Monme is one of the basic units of mass in the shakkanhō system, defined as follows.

Shakkanhō is the system of mass units belonging to the same framework as the length units shaku and sun, and was widely used from the Edo period through the early Showa era in everyday commerce and records of craft objects.

Why Monme Has Been Used for Sword Weight

In commerce involving high-value art and craft objects such as swords and tōsōgu, weight has long been regarded as an indicator of the material's own value. In particular, for tōsōgu made with precious metals such as gold, silver, and shakudō, the amount of base metal used directly determines value, so recording weight in monme had practical significance.

For blades as well, there are examples of monme notation surviving in old catalogs, recorded to document the amount of tamahagane forged or to capture the sense of mass in a finished blade. While gram notation has become standard in modern kanteisho and sales materials, when researching the provenance of old heirloom pieces one may still encounter documents using monme.

Modern Blade Weight and Reference Figures in Grams

In modern practice, gram units are used exclusively. As a reference, the blade alone (without koshirae) typically weighs approximately 600 to 900 grams, and when the complete koshirae including the saya and tsuka is added — the finished piece having its center-of-balance adjusted through sori and cross-section design — the total often comes to approximately 1,000 to 1,400 grams. These are, of course, only reference figures; tachi with long nagasa and deep sori, and tantō with their smaller size, will fall well outside this range.

As a practice in monme conversion, if a blade is recorded as "150 monme," the calculation is 150 × 3.75 = 562.5 grams. Keeping this conversion formula in mind will prove useful when converting figures from old documents into grams.

The Relationship between Kan and Monme — Units for Expressing Greater Weights

While monme is used for the weight of tōsōgu and small items, the larger unit kan is sometimes used for heavier objects such as a full suit of armor or an ōdachi. One kan equals 1,000 monme, or approximately 3.75 kilograms. When weight is recorded in old documents in the form of "some kan, some monme," the kan figure and the monme figure must be read separately.

It should also be noted that monme was originally a unit of mass and also has a history of use as a silver currency unit during the Edo period. Behind the fact that a single word, monme, could refer to both weight and monetary value lies the commercial custom of an era when the weight of precious metals was itself the measure of value. That monme has been used in records of swords and tōsōgu is not unrelated to this sense that weight directly translates into value.

Where Monme Still Appears Today

There are few occasions in everyday modern life to encounter monme, but it can still be seen in the following contexts.

• Descriptions in old sword catalogs and box inscriptions passed down through antique dealers and old families
• Weight notation still used by custom in precious metal shops and pearl trading
• Exhibition notes at local history museums and museums that quote Edo-period records directly

Having a feel for the conversion between monme and grams, so as not to be confused when encountering such old notation in the course of handling swords, is an unassuming but important piece of foundational knowledge for reading documents accurately.

Raising the Resolution of Old Records through Unit Conversion

If one continues pursuing swords as a hobby, the opportunity to encounter catalogs that have emerged from old families or descriptions recorded in old-period sword texts will eventually arise. Many such documents are written in shakkanhō according to the customs of the time, with lengths expressed in shaku and sun and weights in monme and kan. Being able to convert these into metric units as needed raises the resolution of the information the documents are trying to convey by one level.

Conversely, reading old records without knowing monme or the shakkanhō system means one cannot grasp the sense of scale in the numbers and cannot correctly form an image of the swords described. Just like length units, the units of weight are a small but indispensable tool for understanding nihontō as a cultural heritage object within its historical context.

Summary — The Ability to Read Old Units Brings Documents to Life

The unit monme may no longer be the main currency of modern sword transactions, but it lives on as a key to correctly understanding past records and provenance. As long as one has grasped the simple conversion of 1 monme = 3.75 grams, the weight information recorded in old catalogs and box inscriptions can be reinterpreted in modern terms. Together with the shakkanhō notation for nagasa, knowing the traditional units of weight should increase one's means of understanding nihontō as a cultural heritage object in a more three-dimensional way.