There are 0.454 kilograms in a pound, so to convert pounds to kilograms, the number of pounds must be multiplied by 0.454; based on this formula, 166 pounds is equal to 75.364 kilograms. The exact weight of a kilogram is defined as 0.45359237 of a pound, which makes 1 pound equal to roughly 2.2 kilograms.
The kilogram represents the base unit of mass in the International System of Units, or SI. The avoirdupois pound, or international pound, is used as both a U.S. customary and Imperial system unit. The kilogram is the only SI measurement unit that is specifically defined by a physical artifact. The defining artifact itself was commissioned by the General Conference of Weights and Measures in 1875. The prototype, a platinum and platinum-iridium alloy cylinder, is kept at the International Bureau of Weights and Measures near Paris, France.
The kilogram is a unit of mass and it differs from a measurement of weight. Weight is dependent upon the force of gravity exerted on an object while mass remains the same and is independent of gravity. Measurements of mass are usually determined through the use of a weighing scale, by which the weight of the object is compared to the weight of a standard mass, the mass of which is already known in kilograms. The ratio of gravity acting upon the known mass and unknown mass is equal to the ratio of mass between the two objects.