mou, Chinese unit of land measurement that varies with location but is commonly 806.65 square yards (0.165 acre, or 666.5 square metres). Based on the chi, a unit of length after 1860 measuring 14.1 inches, the mou has been defined by customs treaty as 920.417 square yards. In ancient China, where units of measure displayed great regional and functional variety, the mou ranged from 1/30 to 1/8 hectare (333.333 to 1,250 square metres).