Convert electrical current (amps) to power (kilowatts) for AC and DC circuits
Amps (amperes) measure electrical current—the flow of electrons through a conductor. Kilowatts (kW) measure power—the rate of energy consumption or production. Converting between them requires knowing the voltage and, for AC circuits, the power factor.
For DC circuits, the calculation is straightforward: Power = Current × Voltage. For AC circuits, power factor (PF) accounts for the phase difference between voltage and current in inductive or capacitive loads like motors and transformers. Real-world AC loads rarely have a power factor of 1.0.
This calculator handles DC, single-phase AC, and three-phase AC circuits—covering everything from household appliances to industrial motors. It's essential for electricians, engineers, and anyone sizing electrical equipment, circuits, or generators.
Batteries, solar panels, electronics. Power = Amps × Volts. No power factor needed.
Household outlets (120V/240V). Power = Amps × Volts × PF. Most home appliances.
Industrial power. Power = √3 × Amps × Volts × PF. More efficient for heavy loads.
Ratio of real power to apparent power. Motors: 0.80-0.85. Resistive loads: 1.0.
| Application | Voltage | Power Factor | Circuit Type |
|---|---|---|---|
| US Household | 120V | 0.95-1.0 | Single-Phase |
| US Large Appliances | 240V | 0.85-0.95 | Single-Phase |
| European Household | 230V | 0.95-1.0 | Single-Phase |
| Industrial Motors | 480V | 0.80-0.85 | Three-Phase |
| EV Charging (L2) | 240V | 0.95+ | Single-Phase |
| Solar Inverters | 240V | 0.99+ | Single-Phase |
A 15-amp, 120V circuit provides 1.8 kW max. A 20-amp circuit provides 2.4 kW. Use 80% rule for continuous loads.
Total your loads in kW, add 20% margin, then select generator kVA rating (kVA = kW ÷ PF).
Level 2 chargers at 40 amps, 240V deliver 9.6 kW. A 10 kWh battery needs about 1 hour to charge.
A 10 HP motor draws about 15 amps at 480V three-phase. Use nameplate data for accuracy.
Estimating real power for a 50 A motor on a 480 V three-phase service with a typical 0.85 power factor.
Result35.3 kW
Apply kW = (\u221A3 \u00D7 V \u00D7 I \u00D7 PF) / 1000 = (1.732 \u00D7 480 \u00D7 50 \u00D7 0.85) / 1000 \u2248 35.3 kW. A purely resistive load (PF = 1.0) at the same current and voltage would draw \u224841.6 kW, so the 0.85 power factor reduces real power by roughly 15%.
Power factor (PF) is the ratio between real power (kW) and apparent power (kVA). It ranges from 0 to 1. Inductive loads like motors have PF < 1, meaning they draw more current than purely resistive loads for the same power. Low PF wastes energy and requires larger wiring.
Check the nameplate or specifications. For motors, it's typically 0.80-0.90. For resistive heaters, it's 1.0. For LED lighting with drivers, it's usually 0.90+. If unknown, 0.85 is a reasonable estimate for mixed loads.
kW (kilowatts) is real power—what does useful work. kVA (kilovolt-amperes) is apparent power—the total current × voltage. For DC and resistive AC loads, they're equal. For inductive/capacitive AC loads: kW = kVA × PF. Generators are rated in kVA.
Three-phase delivers constant power (single-phase pulsates), uses less copper for the same power (3 wires vs. 2), and runs motors more smoothly. Industrial facilities use three-phase for heavy loads because it's more efficient and cost-effective.
Use DC for batteries, solar panel strings, EV battery packs, and low-voltage electronics—anywhere current flows in one direction. Use AC single-phase for standard outlets and residential wiring (120 V or 230 V), and AC three-phase for commercial or industrial circuits (208 V, 400 V, 480 V). DC ignores power factor; AC requires it.
Resistive loads (heaters, incandescent bulbs): 1.0. LED drivers and modern electronics: 0.90-0.95. Single-phase induction motors: 0.80-0.90 at full load. Three-phase motors: 0.85-0.92. Mixed building loads: 0.85 is a reasonable default. Always prefer nameplate data when sizing real equipment.
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