masu are the wooden square boxes that were traditionally used as a measurement tool in japan.
a full masu is equal to 180ml or what is called a ‘go’.
masu were used to measure important commodities at markets, such as rice, soy sauce, or sake. since people were familiar using the measuring box, it became popular at restaurants to serve sake in masu, so patrons would have no doubt of the amount of sake they were receiving from the proprietor.
four ‘go’ is equivalent to 720ml which is still a standard bottle size in sake production. also known as ‘yongo-bin’
ten ‘go’ is equal to 1.8 L, which are the gigantic sake bottles you might’ve seen at some izakayas. these are also commonly known as ‘issho-bin’.