In China, 1 sho was roughly the same as today's 1 go in the ancient times, and it became roughly the same as today's 3 go in the age of the Tang Dynasty, and around when the unit was introduced into Japan, it became roughly the same as today's 4 go.
古代中国における1升は現代の1合程度であったが、唐代には3合程度になり、日本に伝わるころには4合程度になっていた。