Handbook 652 Body Electrical Diagnosis Measuring Amperage An ammeter is used to measure current flow, also called amperage because it is measured in amperes (amps, for short). To measure amps, current must flow through the ammeter. The circuit must be opened so the ammeter can be placed “ in-line ” with the circuit. Small values of current flow are expressed in milliamps (mA). One amp equals 1000 milliamps. A value of 650 milliamps equals 0.650 amp. Technical Training 27