You can measure millivolts with some voltmeters and multimeters. A voltmeter measures voltage. A multimeter can measure multiple quantities, such as voltage (volts), resistance (ohms) and current (amperes). Meters can be digital or analog. A millivolt is equal to one thousandth of a volt. Make sure your meter has the ability to measure into the millivolt range.
Plug the red probe into the hole marked "V" or "+" on your meter. The hole may be colored red.
Plug the black probe into the hole marked "COM" or "-" on your meter. The hole may be colored black.
Turn the dial on your meter to a milivolt range setting. The setting should be close to but not over the maximum voltage you are measuring. Use the DCV settings if you are measuring a direct current (DC) source, such as a battery. Use the ACV settings to measure alternating current (AC) sources, such as house appliances.
Turn your meter on.
Hold the insulated handles of your probes. Touch the red probe to the positive (+) side of your DC or AC circuit. Touch the black probe to the negative (-) side of the circuit.
Read the measurement from the meter dial or the display screen.