The watt is a unit of power named after the Scottish engineer James Watt. It measures the rate of power conversion and can be calculated by the product of volts and amps: watts = volts x amps. A milliwatt is 1/1000 of a watt, and a millivolt is 1/1000 of a volt. To convert milliwatts to millivolts, you have to know the amps involved in the circuit. An amp is a measure of the amount of electrical charge being passed through a circuit.

Determine the value of amps in a circuit. Assume that a small electronic device can pull 75 milliamps of current. Write the number down.

Determine the value of wattage in the circuit. For example, there are 200 milliwatts available for the electronic device. Write the number down.

Calculate the millivolt value using the following formula: millivolts = milliamps / milliwatts. For this example, the answer is 75 milliamps / 200 milliwatts, or 0.375 millivolts.