Note 1 to entry: 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

length, l	radius, r	radius of circle A, rA or r(A)
	wavelength, λ	wavelength of the sodium D radiation, λD or λ(D; Na)
energy, E	kinetic energy, T	kinetic energy of particle i in a given system, Ti
	heat, Q	heat transferred to a sample i of water, Qi
electric charge, Q		electric charge of the proton, e
electric resistance, R		electric resistance of resistor i, Ri
amount-of-substance concentration of entity B, cB		amount-of-substance concentration of ethanol in wine sample i, ci(C2H5OH)
number of entities, N		number of turns in a given coil i, Ni
Rockwell C hardness, HRC		Rockwell C hardness of steel sample i, HRCi

Note 2 to entry: 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 IEV 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 to entry: 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 IEV 102-03-21, vector quantity, and IEV 102-03-40, tensor quantity).

Note 4 to entry: The concept of quantity may be generically divided into, e.g. physical quantity, chemical quantity, biological quantity, etc., or base quantity and derived quantity.