|Definition:|| property of a phenomenon, body, or substance, where the property has a magnitude that can be expressed by means of a number and a reference
NOTE 1 – The generic concept of quantity can be divided into several levels of specific concepts, as shown in the following table. The left hand side of the table shows specific concepts under ‘quantity’. These are generic concepts for the individual quantities in the right hand column.
NOTE 2 – The reference can be a unit of measurement, a measurement procedure, a reference material (ISO/IEC GUIDE 99:2007 5.13), or a combination of such. The magnitude of a quantity is called "value of the quantity" (see 112-01-28). In the frequent case of a unit of measurement, the magnitude is the product of a number and the unit of measurement.
NOTE 3 – A quantity as defined here is a scalar. However, a vector or a tensor whose components are quantities is also considered to be a quantity (see 102 03 21, vector quantity, and 102-3-40, tensor quantity).
NOTE 4 – The concept of quantity may be generically divided into, e.g. physical quantity, chemical quantity, biological quantity, etc., or base quantity and derived quantity.