Masu (枡 升) is originally a square wooden box for measuring rice in Japan. Masu (枡 升) comes in a variety of sizes from 1 to (斗) (一 斗 枡 ittomasu) (about 18 liters) to 1 go (合) (一 合 枡 ichigomasu) (about 0.18 liters). Masu (枡 升) is used for many different uses, such as for storing dry spices or for drinking Sake (酒). Besides, Japanese artists also create Masu (枡 升) as cute souvenirs.

When ordering sake in bars in Japan, the service will bring out a glass, a wooden cup, a wooden cup is usually square, the sides are smooth and lined, the wood is often used cedar or Lacquer or sometimes plastic, the wooden cup is called masu cup, then the glass cup will be placed inside the masu wooden cup and poured sake until it spills over the masu cup.

During festivals, people often pour sake straight into a masu cup to enjoy, while in bars or restaurants, people often put a glass into the masu cup to pour about half a cup of masu. In Japan, this approach is considered an extremely interesting entertainment and is called Mokkiri Sake.

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As for the rule of using masu cups, there is no specific rule, but to drink politely, we can refer to the steps of drinking Japanese sake with masu cups as follows:

Step 1: Take a small sip of sake from the glass to help fill, at this time both the glass cup and the masu cup are placed on the table.

Step 2: Raise the cup by holding the glass in the right hand and the masu cup in the left hand, to prevent the sake from spilling out, place the masu cup underneath so that the sake can overflow.

Step 3: When the sake in the glass is over, pour the sake in the masu cup into the glass and put the glass inside the masu cup, finally enjoying the rest of the sake in the cup.