We used to use "skaku and sun" which are the fundamental unit of length in Japan.( We use the metric system now.) "Shaku" is 30.3cm and "Sun" is 3.03cm. For the sizes of Bonsai Pots, we still use the unit of sizes called "gou" by using "shaku and sun"so that we can image how big the pot is approximately between maker and wholesaler. For example, "5 gou"is 5 times 3.03cm is 15.05cm. It means "5 gou pot" is about 15cm(135-165mm approximately) wide.