Whose Foot?

Everybody is different. So why do we use feet to measure length?

- By Evelyn Lamb

Maybe you have wondered why 12 inches is called a foot.

Traditional units of distance such as the Iranian parasang and English league both reflect how far a person could walk in a certain amount of time. Ancient Greeks and Romans measured with the foot (pous in Greek and pes in Latin), which was based on the length of the average adult man’s foot.

The units people prefer for measurements change over time. The reasons include convenience, compatibility with other units, and advances in science and technology that allow and require more precise information.

Britain started using the foot during the Roman conquest early in the first millennium. The Roman pes naturalis (“natural foot”) was about 10 inches (25 cm). To compare to shoe sizes, a foot that long would wear a men’s size 7.5 or women’s size 9 shoe in the US sizing system. Then a length close to 12 inches (30.5 cm) became accepted. It was a more convenient definition because it was more compatible with other units. (A 12-inch foot requires a pretty big shoe: a men’s 14 in the US. That’s the size pro basketball player Kawhi Leonard wears.)