Pounds Conversion

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  • lb
  • lbm (pound-mass – scientific)

Unit of:

  • Mass
  • Weight (in non-scientific affairs)

Worldwide use:

  • U.K., U.S.A, Australia, Canada, New Zealand et al


The pound is a measurement of mass used in the imperial system, and is accepted on a day-to-day basis as a unit of weight (the gravitational force acting on any given object).


The imperial (avoirdupois, or international) pound is officially defined as 453.59237 grams.


The name pound is an adaptation of the Latin phrase libra pondo, or a pound weight, the Roman libra (hence the symbol lb) weighed approximately 329 grammes.

Throughout history the pound (or its local translation) has been used as a measurement of weight in many different parts of the world, including The United Kingdom, France, Germany, Scandinavia and Russia. Although the exact mass defined as a pound has varied from system to system, they have been broadly similar, usually between 350 and 560 metric grammes.

In the UK numerous different systems using the pound have co-existed, although the avoirdupois pound (also known as the wool pound) has been the most commonly used and long-lasting (abbreviated to lb av or lb avdp). One variation still used today is the Troy pound (approx. 373g), most often as a mass measurement for precious metals.

The UK Weights and Measures Act of 1878 first defined the imperial pound in terms of metric units (1lb = 453.59265g) , and in 1893 the Mendenhall Order defined the United States pound by describing a kilogram as equivalent to 2.20462 pounds.

The United States and countries of the Commonwealth of Nations agreed common definitions for the pound (and the yard) that were adopted in 1959 (UK 1964).

Common references:

  • In English-speaking countries a person's weight is commonly expressed in stones and pounds, although in the United States this is usually expressed purely in pounds.
  • In the UK and Ireland, foodstuffs commonly sold by the pound prior to the adoption of the metric system are still sold in quantities equivalent to the old imperial standard, such as butter, which is most usually sold in 454g (1lb) packets.
  • Anglers will often express the size of a fish caught in terms of pounds and ounces.
  • Shakespeare's character Shylock famously asked for "a pound of flesh" as assured security for a loan.

Usage context:

Scientific applications use the pound to describe mass, whilst everyday use sees it as a measure of weight. Despite broad acceptance of the metric system of weights and measures, the pound continues to be used in English-speaking countries.

The pound has historically been the means of describing the weight of shot or shells in weaponry, and the weapons themselves came to be named after the ammunition they would fire, for example a 32-pounder.

In the UK and America the pound is also used to help express pressure, with pounds per square inch (p.s.i.) an accepted standard.

Component units:

  • There are sixteen ounces to one pound, although historically (and officially), the pound was defined as comprising 7,000 troy grains (gr) until the agreed international standard was implemented in 1959.