1911 Encyclopædia Britannica/Inch

INCH (O. Eng. ynce from Lat. uncia, a twelfth part; cf. “ounce,” and see As), the twelfth part of a linear foot. As a measure of rainfall an “inch of rain” is equivalent to a fall of a gallon of water spread over a surface of about 2 sq. ft., or 100 tons to an acre.