Watt Calculator

Watts measure electrical power — the rate at which energy is consumed or produced. Amps measure electrical current — the flow rate of electric charge. They are related by voltage: P (W) = V (volts) × I (amps). You need both voltage and current to determine power.

Kilowatts (kW) is a unit of power — the rate of energy use at a given instant. Kilowatt-hours (kWh) is a unit of energy — the total energy consumed over time. Running a 1 kW appliance for 2 hours uses 2 kWh of electricity.

Power factor (PF) applies to AC circuits and represents the ratio of real power (W) to apparent power (VA). In a purely resistive circuit PF = 1. Inductive loads like motors have a PF less than 1, meaning they draw more current than their watt rating alone suggests. Real power = V × I × PF.

1 mechanical horsepower equals exactly 745.7 watts. This conversion is commonly used when sizing electric motors, generators, and vehicle engines. The metric horsepower (PS) is slightly different at 735.5 W.

Use P = V × I when you have a multimeter and measured both voltage and current. Use P = I²R when you know current and resistance (e.g., in a simulation). Use P = V²/R when you know voltage across a known resistor. All three give identical results for resistive circuits.