Kilogram

The kilogram is the SI unit of mass. Earlier definitions of units of mass in the metric system started with the gram, which is one-thousandth of a kilogram. The first definition of a gram was the weight of 1 cm³ of water at its maximum density (at 4 degrees C); the kilogram was the weight of 1,000 cm³, or 1 dm³ of water. Since then, the kilogram has been defined by the weight of a prototype cylinder kept at Sevres, France.