The number of ohms in a circuit describes the circuit's resistance to current. This value is the ratio between the circuit's voltage, which is the potential difference in charge across it, and its current, which is its rate of flow of charge. The number of kilowatts that go through a circuit is the rate at which the circuit transfers energy. A circuit's power rating is the product of its voltage and current, but if you know its resistance, you only need to know one other of these variables to calculate the power rating.

Square the circuit's voltage. For example, if the circuit runs at a voltage of 120 volts, then 120² = 14,400 V².

Divide this answer by the circuit's resistance, measured in ohms. For example, if the circuit has a resistance of 24 ohms, then 14,400 ÷ 24 = 600 volt-amperes, or 600 Watts.

Divide this answer by 1,000, which is the number of Watts in a kilowatt: 600 ÷ 1,000 = 0.6. This is the power running through the circuit, measured in kilowatts.