Calculate DC, single-phase or balanced three-phase power with power factor, efficiency, energy use, horsepower and optional cost.
Physics & electrical calculator
See real, apparent and reactive power, efficiency-adjusted output, energy use and optional electricity cost.
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Electrical power
Power, energy and cost results will appear here after valid circuit values are entered.
Methodology
DC real power uses P = VI. Single-phase AC uses P = VI·PF, while balanced three-phase uses P = √3·Vₗₗ·I·PF. Apparent power omits PF, reactive power follows the power triangle and useful output equals real input multiplied by efficiency.
Worked example
At 400 V line-to-line, 10 A and 0.8 power factor, balanced three-phase real power is √3 × 400 × 10 × 0.8 ≈ 5.543 kW. Running eight hours daily for 30 days uses about 1,330.2 kWh.
Do not mix power quantities
Real power does useful work, apparent power sizes the total voltage-current demand and reactive power completes the AC power triangle. The calculator reports each separately so a low power factor is not hidden.
Relationship reference
The Open University electronics material summarizes power = voltage × current and the watt as joule per second. The AC modes extend that base relationship with phase and power-factor terms.
Open University: electrical quantity relationshipsRelated physics tools
Common questions
For steady DC, real power is voltage multiplied by current: P = V × I. One watt equals one joule per second.
Using RMS voltage and current, real power is V × I × power factor. Apparent power is V × I in volt-amperes.
With line-to-line voltage and line current, apparent power is √3 × V × I and real power also multiplies by power factor.
Reactive power represents energy exchanged with inductive or capacitive fields. The calculator derives it from Q = √(S² − P²) for the entered apparent and real power.
No. Power factor relates real power to apparent power in AC. Efficiency relates useful output power to real input power. They describe different losses or effects.
Real input power is converted to kilowatts and multiplied by hours per day, days and the entered price per kWh. Taxes, tiered tariffs and demand charges are not added automatically.
The AC calculations assume sinusoidal, balanced operation and consistent RMS line values. Harmonics, unbalance, motor starting and tariff demand charges require additional analysis. This calculator is for planning and education, not personal financial advice.