Dimensions of a physical quantity are the power to which the fundamental quantities must be raised to represent the given physical quantity.
Thus, the dimensions of density are 1 in mass and –3 in length. The dimensions of all other fundamental quantities are zero.
For convenience, the fundamental quantities are represented by one letter symbols. Generally mass is denoted by M, length by L, time by T and electric current by A.
The thermodynamic temperature, the amount of substance and the luminous intensity are denoted by the symbols of their units K, mol and cd respectively. The physical quantity that is expressed in terms of the base quantities is enclosed in square brackets.