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Devised by Romans based on width of the thumb

Symbol: in / Base data: Imperial units.
1 inch = 2.54 cm

Foot is divided into 12 sections

This unit derives from the width of a thumb. The Romans established that multiplying the width of a thumb by 12 times would be equivalent to the length of a foot. The word “inch” derives from “uncia”, which means one-twelfth in Latin. The British called this length a “thumb” in ancient times, saying that it was equivalent to three grains of barley.