Which instrument measures electric current in a circuit?

An ammeter measures electric current in a circuit.

Its name combines “ampere,” the SI unit of electric current, with “meter.” An ammeter is connected in series so that the circuit current passes through its sensing element. An ideal ammeter would have zero resistance; real instruments are designed with very low resistance to minimize the disturbance they cause.

Traditional analog ammeters used moving-coil or moving-iron mechanisms. Modern digital multimeters measure current electronically, often through a precision shunt resistor and an internal measuring circuit. Large currents may be measured indirectly with a current transformer or a clamp meter.

A voltmeter is connected in parallel and measures potential difference, so confusing the two instruments can create an incorrect reading or damage equipment. Many multimeters require moving a test lead to a separate current terminal because current measurements can bypass much of the instrument’s normal resistance.