The number of watts within an electrical system is determined by the product of the voltage and amperage within the electrical system. The overall value returned is proportionate to both voltage and amperage. Due to this relationship, a measurement of watts does not provide a very detailed accounting of the properties within the electrical system being examined. It is possible, however, to work backwards and determine the voltage and amperage properties within the system.

Multiply the number of megawatts by 1 million. This reduces the unit to single watts.

Divide the number of watts by the voltage at which the system runs.

Simplify the final answer. Specifically, the units of voltage cancel out leaving only amperage. The final result may be divided by 1000 or 1 million to express the number of amps in kilo-amps or mega-amps.