EXPLAINER: Why is ‘pound’ abbreviated as ‘lb’ when neither letter appears in the word?

You’ve seen it everywhere: a 10-pound dumbbell is marked 10 lb. A 50-pound bag might say 50 lb.

But there’s something strange about it.

Where did the “l” and “b” come from?

The answer is roughly 2,000 years old.

Blame the Romans

The abbreviation “lb” traces back to ancient Rome and the Latin word libra, associated with scales, balance and a Roman unit of weight.

The Romans also used the expression libra pondo, essentially referring to a pound by weight. Pondo is related to the Latin verb pendere, “to weigh.”

As the terminology evolved into English, something curious happened: the spoken name eventually became “pound,” while the abbreviation associated with libra survived as “lb.”

That is why the letters don’t seem to match the English word at all.

And that’s not libra’s only legacy

The British pound sign £ also traces its shape to a stylized letter L, historically connected with libra.

There’s another fascinating typographic connection: the old abbreviation for pound was sometimes written ℔, with a stroke through or above the letters. This mark is widely cited as an ancestor of the # symbol—which helps explain why Americans have traditionally called # the “pound sign.”

‘Lb’ is still very much alive

The pound remains widely used, particularly in the United States. Since an international agreement in 1959, the international avoirdupois pound has been defined as exactly 0.45359237 kilogram.

And while people commonly write “lbs” for the plural, technical style generally treats unit symbols as unchanged: 1 lb, 10 lb, 100 lb.

So the next time you wonder why “pound” becomes “lb,” remember: you’re looking at a tiny linguistic fossil from ancient Rome that survived into the modern world.

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