Kilogram
Symbol: kg
The kilogram is the base unit of mass in the International System of Units. The prefix "Kilo" is given from the Greek word "chilioi" for thousand. SI prefixes are used with the gram, not the kilogram, which already has a prefix as part of its name. For instance, one-millionth of a kilogram is 1 mg (one milligram), not 1 µkg (one microkilogram).
The kilogram is defined as being equal to the mass of the International Prototype Kilogram (IPK). It is a cylinder of 39mm height and diameter, consisting of 90% platin and 10% iridium. The IPK is stored in a vault at the BIPM in Sèvres, France.