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# Difference between pound and kilogram (kg vs lbs)

Pounds and kilograms are two of the many units used for the measurement of mass. Physical quantities need units for their measurement. We need standard well-defined units for measurement of physical quantities.

Although both pound and kilogram are units of mass but there are some profound differences between these two units of mass. A pound is a unit of measuring mass that belongs to the imperial system of units. A kilogram on the other hand is a SI unit of mass.
Before looking at the difference between pound and kilogram let us first get an idea about kilogram and pound mass.

## Kilogram Definition

One kilogram is equal to the mass (a platinum-iridium alloy cylinder) kept at International Bureau of Weights and Measures, at Sevres, near Pairs, France.
Originally 1 Kg was defined as the mass of 1 liter of water at $4^0C$ because at $4^0C$ water has maximum density and maximum volume.

## Pound Definition

Pound or pound-mass (written as lb) like Kilogram is also a unit of measurement of mass used in imperial (FPS system of unit ), United States customary.

The Avoirdupois system is used to define the mass of 1lb of weight. The avoirdupois system (abbreviated avdp) is a measurement system of weights that uses pounds and ounces as units.

The United States and countries of the Commonwealth of Nations agreed upon common definitions for the pound and the yard. Since 1 July 1959, the international avoirdupois pound has been defined as exactly 0.45359237 kg. For most calculations purpose we consider
1 pound mass = 0.45 Kg