"lbs" and "pounds" are the same thing
There is no conversion here. "lbs" is simply how pounds is written short, so 5 lbs equals 5 pounds equals 0.4536 kg either way. The abbreviation looks odd only because it does not come from the English word at all.
Where the strange abbreviation comes from
- libra. The Roman unit of weight, and also their word for a balance scale. "lb" is short for libra, and the ℔ sign is a struck-through l for the same word.
- lb vs lbs. Strictly, lb is the singular and lbs the plural, so "1 lb, 5 lbs." In practice people write lbs for both and standards bodies quietly prefer lb everywhere.
- The £ connection. The pound sterling symbol is a decorated L, also from libra, dating to when a pound of silver was a pound of money.
The one real distinction: pounds of mass vs pound-force
Everyday "pounds" measure mass, exactly like kilograms. Engineers sometimes need the force that mass exerts under gravity, and they write that as lbf.
- lb / lbm — mass. Your body weight, a bag of flour, shipping weight. This is what "pounds" means almost everywhere.
- lbf — pound-force. Used for torque (lbf·ft), pressure (psi is pounds-force per square inch) and thrust. One pound of mass weighs one lbf at Earth's surface, which is why the two are so easily blurred.
- Not fluid ounces. A pound is 16 ounces of weight, not 16 fluid ounces of volume — a separate ounce that happens to share the name.
Common questions
Is lbs the same as pounds?
Yes, exactly. "lbs" is just the written abbreviation for pounds. 5 lbs and 5 pounds are the same weight; there is nothing to convert between them.
Why is pounds abbreviated lb when there is no "l" or "b" in the word?
It comes from the Latin word libra, meaning a pound weight or a balance scale. "lb" is short for libra, and adding an s just marks the plural. The same libra is why the British pound sign is a stylised L.
What is the difference between lb and lbf?
lb (or lbm) is a unit of mass. lbf, pound-force, is the force that mass produces under gravity. In everyday use "pounds" means mass; lbf only shows up in engineering, for things like torque and pressure.
