# Why isn’t 1 lb exactly 500 g? Where does lb come from?

Last Updated : 01 Feb, 2024

The pound, rooted in Roman and Anglo-Saxon units of weight, was standardized as 453.592 grams. The gram, however, is a metric unit, defined much later with the metric system’s establishment, based on the mass of one cubic centimeter of water.

## Answer: 1 pound (lb) is not exactly 500 grams (g) because they originate from different measurement systems with distinct historical bases.

• Different Measurement Systems:
• The pound is part of the imperial system of measurements, historically used in British and now predominantly in the United States.
• The gram is part of the metric system, which is based on a decimal system and is used worldwide.
• Historical Origin of Pound (lb):
• The term “pound” comes from the Roman unit of measure “libra pondo,” meaning “a pound by weight.”
• The Roman libra was quite close to the current definition of a pound but was not is the same.
• Current Definition:
• 1 pound is legally defined as exactly 0.45359237 kilograms.
• Since 1 kilogram equals 1000 grams, 1 pound equals approximately 453.59237 grams, not 500 grams.

### Hence, the slight difference between 1 pound and 500 grams reflects the historical development and standardization of measurement systems over time.

The metric system, with its decimal-based approach, was designed for simplicity and universal adoption, while the imperial system evolved from the varied units used in the British Empire.

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