Three-Phase Power Calculator
Calculate apparent power (kVA), real input power (kW), and reactive power (kVAr) for a balanced three-phase AC load using line-to-line voltage, line current, and power factor.
Enter electrical values
Results
Apparent power— kVA
Real input power— kW
Reactive power— kVAr
Estimated output power— kW
Output power is shown only when efficiency is entered. It is an estimate, not a substitute for measured motor or driven-equipment performance.
Three-phase power formulas used
For a balanced three-phase system using line-to-line voltage and line current:
kVA = √3 × V × I ÷ 1000
kW = √3 × V × I × PF ÷ 1000
kVAr = √(kVA² − kW²)
If efficiency is entered, the calculator estimates useful output power as:
Estimated output kW = input kW × efficiency
Worked example
For a balanced 400 V three-phase load drawing 50 A at 0.85 power factor:
| Quantity | Calculation | Approximate result |
|---|---|---|
| Apparent power | 1.732 × 400 × 50 ÷ 1000 | 34.64 kVA |
| Real input power | 34.64 × 0.85 | 29.44 kW |
| Reactive power | √(34.64² − 29.44²) | 18.26 kVAr |
How to use the result in maintenance
- Compare calculated input power with normal historical readings to investigate abnormal loading.
- Use measured voltage, current and power factor rather than nameplate assumptions when diagnosing an operating system.
- Compare phase currents separately before treating a three-phase load as balanced; significant imbalance needs separate investigation.
- For motors, remember that electrical input kW is not the same as mechanical shaft output kW because losses occur in the motor.
- For VFD-fed motors, harmonics and drive behavior can make simple hand calculations less representative than readings from a suitable true-power instrument.
Engineering and safety limitation: This calculator is an educational tool for balanced three-phase systems. Do not use it to select protective devices, cables, switchgear, transformers, generators or safety settings without a competent electrical design review. Approved drawings, applicable regulations, OEM data, site procedures, PTW/LOTO requirements and calibrated measurements take priority.
Common mistakes
- Using phase-to-neutral voltage when the formula expects line-to-line voltage.
- Entering power factor as 85 instead of 0.85.
- Assuming a motor's nameplate kW is its present electrical input power.
- Ignoring phase imbalance, voltage distortion or VFD harmonics.
- Using estimated efficiency as though it were a measured value.
Related learning
VFD FundamentalsUnderstand drive operation, speed control and structured fault checks.Electrical TroubleshootingContinue into the industrial electrical maintenance learning path.Professional PPM ChecklistTurn electrical inspection requirements into measurable maintenance tasks.
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