Why lb Is the Symbol for Pounds:

Have you ever wondered why we use the symbol "lb" for the "pounds" unit? The word "pound" is short for "pound weight," which was libra pondo in Latin. The libra part of the phrase meant both weight or balance scales. The Latin usage was shortened to libra, which naturally was abbreviated "lb". We adopted the pound part from pondo, yet kept the abbreviation for Libra.

There are different definitions for the mass of a pound, depending on the country.

In the United States, the modern pound unit is defined to be 2.20462234 pounds per metric kilogram. There are 16 ounces in 1 pound. However, in Roman times, the libra(pound) was about 0.3289 kilograms and was divided into 12 uncia or ounces.

In Britain, there has been more than one type of "pound", including the avoirdupois point and Troy pound. A pound sterling was a tower pound of silver, but the standard was changed to the Troy pound in 1528. The tower pound, merchant's pound, and London pound are obsolete units. The Imperial Standard Pound is defined as having a mass equal to 0.45359237 kilograms, which matches the definition of the international pound, as agreed upon (although not adopted by the U.S.) in 1959.