Pound (mass)

The pound is a unit used to measure mass. Mass is the amount of matter inside an object.

In the modern world, the most common version is the international avoirdupois pound. This unit is used in the United States customary system and the British imperial system. It is officially divided into 16 avoirdupois ounces. Scientists and traders use different symbols to represent it. The standard symbol is "lb." To avoid confusion with force, people sometimes use "lbm," which stands for pound-mass. In the United States, some people use the symbol "#." These symbols help ensure that everyone understands exactly what is being measured during trade or science experiments.

The history of the pound reaches back to ancient Rome. The symbol "lb" comes from the Roman word "libra." This word refers to a scale or a balance. The English word "pound" is also related to this Roman origin. It shares roots with words in German, Dutch, and Swedish.

Over many centuries, different countries developed their own versions of the pound. These versions were not always the same size. Some were used for coins, while others were used for goods like wool. This variety meant that people had to create specific rules to keep measurements fair and accurate.

There are several distinct types of pounds that have existed throughout history. The avoirdupois pound, also called the wool pound, became common around the year 1300. It was eventually redefined during the reign of Queen Elizabeth I to equal 7,000 grains. Another type is the troy pound. This system is smaller, containing only 12 troy ounces and 5,760 grains. While the troy pound is no longer a legal unit for general trade, it is still used for precious metals. Jewelers use troy ounces to weigh gems like opals and metals like gold or silver.

A third type was the tower pound. This was used in England for coinage and was once known as the Saxon pound.

The tower pound has a very specific connection to money. Before the Norman conquest in 1066, the Saxon pound of silver helped set the weight for the pound sterling. King Offa of Mercia used this standard to mint 240 silver pennies. This created a system where twelve pennies equaled a shilling, and twenty shillings equaled a pound. The tower pound was kept at the Tower of London as a standard. However, things changed during the reign of King Henry VIII. In 1526, a royal proclamation required that the troy pound be used for minting money instead of the tower pound.

In the United Kingdom, the government used Acts of Parliament to regulate weights. This was done to prevent fraud in the marketplace. The Weights and Measures Act of 1878 was a major overhaul of these rules. It established a physical standard for the imperial pound. This standard was a platinum cylinder. It was nearly an inch high and had a diameter of about half an inch. The edges were carefully rounded. It even had a groove so an ivory fork could lift it safely.

This cylinder was stamped "P.S. 1844, 1 lb" to show it was the Parliamentary Standard.

As science advanced, the way we define the pound changed from physical objects to mathematical constants. In 1959, the United States and the Commonwealth of Nations reached an agreement. They created the international avoirdupois pound. This version is defined as exactly 0.45359237 kilograms. This was a very important step for international trade. It meant that different countries could use the same numbers. In the United Kingdom, the Weights and Measures Act of 1963 updated the law to match this international standard. Today, the 2019 revision of the SI system defines the pound using fundamental constants rather than a metal object.

The pound remains a significant part of modern life despite the rise of the metric system. In the United States, the Metric Conversion Act of 1975 named the metric system as "preferred." However, it did not stop the use of customary units. The United States is the only industrialized country where commercial activities do not mostly use the metric system.

Even in the United Kingdom, where metrication is common, the European Commission allowed dual marking. This means both metric and imperial units can appear on packaged goods. The pound continues to serve as a bridge between ancient Roman traditions and our modern global economy.