property of a phenomenon, body, or substance, where the property has a magnitude that can be expressed as a number and a reference
NOTE 1 The generic concept '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.
radius of circle A, rA or r(A)
wavelength of the sodium D radiation, λD or λ(D; Na)
kinetic energy, T
kinetic energy of particle i in a given system, Ti
heat of vaporization of sample i of water, Qi
electric charge, Q
electric charge of the proton, e
electric resistance, R
electric resistance of resistor i in a given circuit, Ri
amount-of-substance concentration of entity B, cB
amount-of-substance concentration of ethanol in wine sample i, ci(C2H5OH)
number concentration of entity B, CB
number concentration of erythrocytes in blood sample i, C(Erys; Bi)
Rockwell C hardness, HRC
Rockwell C hardness of steel sample i, HRCi
NOTE 3 Symbols for quantities are given in the ISO 80000 and IEC 80000 series Quantities and units. The symbols for quantities are written in italics. A given symbol can indicate different quantities.
NOTE 4 The preferred IUPAC-IFCC format for designations of quantities in laboratory medicine is “System—Component; kind-of-quantity”.
EXAMPLE “Plasma (Blood)-Sodium ion; amount-of-substance concentration equal to 143 mmol/l in a given person at a given time”.
NOTE 5 A quantity as defined here is a scalar. However, a vector or a tensor, the components of which are quantities, is also considered to be a quantity.