Resistance, measured in ohms, quantifies how a circuit resists the flow of electrical current. Combined with voltage (the electric potential difference) and current, it determines the power delivered or consumed. When the resistance is known, the power can be calculated directly from voltage alone, thanks to Ohm’s Law and the power formula.

Power from Resistance and Voltage

For a purely resistive load, the power in watts is given by:

P (W) = V² / R

To express the result in kilowatts, simply divide the wattage by 1,000.

Step‑by‑Step Example

1. Square the voltage. If the circuit operates at 120 V, compute 120² = 14,400 V².
2. Divide by the resistance. With a resistance of 24 Ω, 14,400 ÷ 24 = 600 W.
3. Convert to kilowatts. 600 W ÷ 1,000 = 0.6 kW.

Thus, a 120‑V circuit with 24 Ω resistance delivers 0.6 kW of power.

These calculations assume a steady, purely resistive load; in AC circuits or those with reactive components, power factor must be considered. For AC, use P = V × I × PF where PF is the power factor.