Physical Quantity

A physical quantity, or simply quantity, is a property of a material or system that can be quantified by measurement. The cited article explains that a physical quantity can be expressed as a value, which is a pair of a numerical value and a unit of measurement, giving the example that the quantity mass can be quantified as a number of kilograms, and that vector quantities have, besides numerical value and unit, a direction or orientation in space. It is the general concept under which the base quantities and every derived quantity fall. Units that measure a derived quantity, one built from the base quantities, are grouped under this general concept.