Electric current is a fundamental quantity. Fundamental quantities are those quantities that cannot be defined in terms of other physical quantities. They are the basic building blocks from which other physical quantities are derived. Electric current is one of the seven fundamental quantities in the International System of Units (SI), along with length, mass, time, temperature, amount of substance, and luminous intensity. Heat capacity, torque, reactance, and density are all derived quantities, meaning they can be expressed in terms of one or more fundamental quantities.