Page "Physical quantity" Paragraph 39

Most physical quantities include a unit, but not all-some are dimensionless.

Neither the name of a physical quantity, nor the symbol used to denote it, implies a particular choice of unit, though SI units are usually preferred and assumed today due to their ease of use and all-round applicability.

For example, a quantity of mass might be represented by the symbol m, and could be expressed in the units kilograms ( kg ), pounds ( lb ), or Daltons ( Da ).