In a Word: Give an Inch, Take an Ounce

Our system of measurement goes back to the Roman Empire, even if the exact lengths and weights have changed.

Older man measuring things using an antique scale
Razoomanet / Shutterstock

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Managing editor and logophile Andy Hollandbeck reveals the sometimes surprising roots of common English words and phrases. Remember: Etymology tells us where a word comes from, but not what it means today.

Building a regular system of weights and measures is no simple task, and different societies did it in different ways. The Roman Empire used a system that divided units into 12 smaller parts. Derived from the Latin unus, meaning “one,” the word uncia meant “one-twelfth part,” and it got a lot of usage in the Roman measurement system.

Like modern Americans, the Romans used the foot as a measurement — only they called it pes, the Latin word for “foot.” They would have used the pes and its uncia division during the second century A.D. to design and build, for example, Hadrian’s Wall, the nearly 80-mile-long stretch of ramparts, forts, castles and settlements in what is now northern England. During the expansion of the empire, Roman forces occupied parts of Britain for more than 350 years, so it’s no surprise, then, that uncia found its way directly from Latin into Old English as ince or ynce, which became, in Modern English, inch.

Though the relationship between inches and feet is the same today as it was 2000 years ago, the exact lengths aren’t the same. A Roman foot was about two-thirds of an inch shorter than the modern foot. Perhaps those Romans had slightly tinier toes?

Uncia was used not only for measurements of length, but of weight as well. The Roman pound was, in Latin, the libra — incidentally, the source of both the abbreviation lb. and the stylized L that is the symbol for the British pound sterling, ₤. For whatever reason, an uncia of a libra — one-twelfth of a pound — didn’t find itself adopted directly into English. The French, however, took it up. This uncia became the Middle French unce, which was later adopted into Middle English and became our ounce.

So, in brief, inch and ounce derive from the same Latin source word.

But that’s not the whole story: Because you’re an astute reader, you stand ready to point out that a pound contains 16 ounces, not 12. And you’re right!

During the Middle Ages, a weight-measuring system was developed in France that, like the Roman system, divided a pound into 12 ounces. Today, this is known as the Troy measurement system — probably after the French city of Troyes, not the ancient city of Troy.

But around the same time, a different system was developed that divided the pound into 16 units — but they kept the same names. Today we call that more common system avoirdupois (from a French phrase meaning “goods sold by weight”), in which there are 16 ounces in a pound — as well as 16 drams in an ounce. The avoirdupois system has largely superseded the Troy system, which today is used for weighing precious metals and gems, but not much else.

Featured image: Razoomanet / Shutterstock

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