A kilogram is approximately 2.20 pounds. The kilogram is the base unit the metric system uses for mass. Beginning in July 1959, the internationally accepted standard for the avoirdupois pound became exactly 0.45359237 kg.
The metric system developers originally defined the kilogram as the mass of 1,000 cubic centimeters of water, but found that standard too difficult to match due to the variations in the density of water with temperature changes. In the late 1800s, scientists created a platinum alloy cylinder equivalent to the kilogram mass. This cylinder soon became the standard for the kilogram. A second cylinder of identical materials and size replaced the first cylinder in 1889, becoming the new standard for the kilogram. As of 2014, this second cylinder remains the standard for the kilogram.