Converting pounds to kg is one thing, but exactly what is pounds and kilos?

Let´s start with the pounds definition..



The Pound, also referred to as pound-mass, is a unit of mass and is used in the imperial, United States customary and also other systems of measurement. 

The exact definition of the pound today according to the avoirdupois ( a system based on a pound of 16 ounces) is exactly 0.45359237 kilograms (kg).

The abbreviation for the pound is “lb” and comes from Roman libra, since the unit pound is an descendant from this. It’s also common to see the abbreviation “lbs” for pounds.

The name pound is a Germanic adaptation of the Latin phrase libra pondo, a pound by weight. 

The Pound historically has varied a lot since there has been many different kinds of pound. For example the Imperial Standard Pound, Troy pound,  tower pound, London pound and so on..

When we say we want to convert pounds to kg today anyway, we usually mean the avoirdupois definition to the current standard definition of kilos (kg).

So one pound = 0.45359237 kilograms (kg).

So if you as an example want the 120 pounds kg representation that’s 120 x 0.45359237 =  54.4310844 kg.



Enough about the pound, and on to the definition of Kilograms (aka kilos or kg). First of all kilo´s definition is one thousand (1000), so kilogram actually means 1000 grams. 

Now the old definition of 1 kg was the mass of 1 liter of water at the temperature of 4 degrees celsius ( 39.2 degrees Farenheit ) but this definition was found to be to inexact.

The new definition is defined by an object called the International Prototype Kilogram(IPK) and is stored at the International Bureau of Weights and Measures. The IPK is made of 90% platinum and 10% iridium (by mass) to minimize oxidation and has two times the density of lead.

International Prototype Kilogram

International Prototype Kilogram

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