In the Edo period, gold, silver, and copper cash served as the basic mediums of exchange. Gold and silver were used for larger transactions, copper cash for smaller ones. The shogunate tried to maintain a stable rate of exchange between the different mediums. Official rates established in 1700 set the value of 1 ryō in gold (also known as 1 koban) at 60 monme in silver, or 4,000 mon in copper coins. In practice, exchange rates varied over time and in different locales. Most notably, the value of copper cash relative to gold and silver declined steadily, so that by Buyō’s time, 1 ryō in gold was equal to about 6,500 coppers. Silver fluctuated less; between 1800 and 1816, 1 ryō equaled between 61 and 67 monme.
Rice prices were in principle geared to the basic currency units, with 1 koku (theoretically the amount consumed annually by an adult male) equal to 1 ryō or 60 monme, but they too fluctuated, and in times of famine the value of 1 koku could easily top 100 monme. Between 1800 and 1816, the value of 1 koku varied between 50 and 70 monme.
The major monetary units in late Edo were as follows:
gold: 1 ryō (or koban) = 4 bu = 16 shu = 400 hiki
silver: ca. 60 monme = 1 ryō gold
copper: ca. 6,500 mon = 1 ryō gold
1 kanmon = 1,000 mon (coppers)