Find real electrical power from current and voltage, or reverse the calculation to find current. Choose DC, single-phase AC or balanced three-phase AC.
Enter the electrical quantities you know
Choose Amps to watts or Watts to amps. Enter current in A, mA or kA, or real input power in W, kW or MW. Supply the operating voltage. For AC, use RMS voltage and the equipment's power factor. DC ignores the power-factor field.
For balanced three-phase AC, select whether voltage is measured line to line or line to neutral. Current is line current; power is the total across all three phases. Single-phase AC ignores the three-phase voltage-type selection. The comparison table uses the same circuit, voltage and power factor as the main result.
Watts, volt-amperes, and power factor
Watts represent real power. Volt-amperes represent apparent AC power. Power factor is real power divided by apparent power, and is not the same as efficiency. A load drawing 10 A at 120 V with a power factor of 0.8 has 1,200 VA of apparent power and 960 W of real power.
Use real electrical input power for the reverse calculation. If only a motor's shaft-output rating is known, electrical input also depends on efficiency. This tool does not infer efficiency, starting current, load imbalance or individual phase values. Its power-factor range is 0.001 through 1; a zero-power-factor load cannot be reversed from real watts alone.
Interpreting three-phase voltage
For a balanced sinusoidal system, line-to-line voltage is √3 times line-to-neutral voltage. The two formula choices agree when the voltage is converted correctly. Entering 400 V as line-to-neutral when it is actually a line-to-line rating changes the answer substantially. These calculations describe the entered operating point; they do not select cable or protective-device ratings.
Schneider Electric's balanced-system power calculation reference explains total power and equal phase assumptions.
Formula
DC: P = V × I
Single-phase AC: P = V × I × PF
Balanced three-phase: P = √3 × V(line-line) × I × PF
Balanced three-phase: P = 3 × V(line-neutral) × I × PF
Reverse: I = P ÷ (voltage × phase multiplier × PF)
Examples
A DC load
12 V × 5 A = 60 W. Power factor does not apply to this steady DC calculation.
A balanced three-phase load
At 400 V line-to-line, 10 A and PF 0.8, total real power is approximately 5,542.5626 W, and apparent power is 6,928.2032 VA.
Precision and definitions
Calculations retain unrounded values internally. Displayed digits do not increase the accuracy of measurements. NIST unit definitions provide the conversion reference.