Electrical Power Calculator - Watts, Volts, Amps for DC, Single & Three-Phase
Electrical Power Calculator
Watts, volts and amps for DC, single-phase and three-phase circuits
Three Systems
Direct current, single-phase household AC and three-phase industrial supplies.
Any Two Values
Start from voltage and current, power and voltage, or any other pair.
Real, Apparent, Reactive
See watts, volt-amperes and vars, which matter when sizing cables, breakers and generators.
Private
Calculated in your browser.
Power Formulas
For DC, P = V × I = I2R = V2/R. In AC, current and voltage can be out of step, so real power is P = V × I × PF, where the power factor PF is between 0 and 1. The product V × I is the apparent power S in volt-amperes, and the reactive power Q = √(S2 − P2) is energy that sloshes back and forth without doing work.
For a balanced three-phase load, P = √3 × VLL × I × PF, using the line-to-line voltage (400 V in Europe, 208 V or 480 V in North America). Example: a 230 V single-phase load drawing 10 A at PF 0.9 uses 2.07 kW of real power and 2.3 kVA of apparent power. Always use the nameplate rating and local electrical code when sizing real installations.
Key Takeaways
- Power factor: Use 1 for resistive loads; motors and power supplies are lower.
- Line-to-line voltage: Three-phase formulas use the voltage between two lines.
- Size for VA: Cables, UPS units and generators are rated by apparent power.