Mass Background

Mass is measured fundamentally in English units in pounds-mass and in Metric units as kilograms.  The kilogram was first defined as the mass of one cubic decimeter of pure water at 4 ^oC.  Today, it is defined as the mass of a solid cylinder of platinum-iridium alloy at this same mass.  The English unit of pounds-mass is defined in terms of the kilogram as 2.204 kg.  The symbol for the pound, lb., comes from the ancient Roman mass measurement abbreviation for the libra.