The seven strictly defined basic units are: length (meter), mass (kilogram), time (second), current (ampere), thermodynamic temperature (Kelvin), amount of substance (mole) and luminous intensity (Candeira).

The unit of measurement refers to the scalar defined and adopted according to the convention, and any other similar quantity can be compared with it so that the ratio of two quantities can be expressed by a number. The unit of measurement has the name and symbol given according to the agreement.