Last modified on 25 January 2012, at 15:55


A dimensionless quantity or number, also called a pure number, is a quantity having no physical dimension. That is, it is the same regardless of the units of measurement used. A dimensionless number can be, but is not necessarily, a ratio of two quantities having the same physical dimensions. For example, strain is the ratio of two quantities expressed in units of length and is thus dimensionless.