Example 1: 400 V motor feeder
For a balanced three-phase load with 400 V line voltage, 25 A line current, and 0.90 power factor:
P = sqrt(3) x 400 x 25 x 0.90 = 15588.46 W
The active power is about 15.59 kW.
Three-Phase Power Calculator
Balanced three-phase power: P = sqrt(3) x V x I x PF
Introduction
Three-phase systems are widely used in industrial and commercial electrical installations because they transmit power efficiently and support large rotating equipment such as motors, pumps, compressors, and process machines. Compared with single-phase systems, three-phase power provides smoother power transfer and is better suited to heavier loads and distribution networks.
This calculator estimates active power in a balanced three-phase system using line voltage, line current, and power factor. It is useful for load estimation, equipment selection, and quick checks during system design or troubleshooting.
It can also support faster feeder, breaker, and equipment planning by turning common three-phase measurements into a straightforward power estimate.
Formula
Balanced three-phase active power: P = sqrt(3) x V x I x PF
Where: use line voltage and line current for a balanced three-phase system
Where: use line voltage and line current for a balanced three-phase system
Variable Definitions
P = active power in watts
V = line voltage in volts
I = line current in amperes
PF = power factor of the balanced load
Units
Line voltage is entered in volts, line current in amperes, and power factor as a decimal between 0 and 1. The calculated power is returned in watts.
Worked Examples
Example 2: 415 V distribution load
For a 415 V system carrying 60 A at a power factor of 0.85:
P = sqrt(3) x 415 x 60 x 0.85 = 36668.61 W
The active power is about 36.67 kW.
How To Interpret Three-Phase Power
The result tells you the real power delivered to the load, not just the apparent loading based on voltage and current. That makes it useful when selecting breakers, feeders, transformers, generators, and motor-control equipment. A low power factor can make the current look high compared with the useful kilowatt output, so this formula helps users understand why two systems with the same amperes may not be delivering the same real power.
For design work, this calculation is usually one step in a chain. After estimating active power, many engineers move on to current checks, cable sizing, voltage drop review, and power-factor correction. That is why this page works best as a practical starting point for broader three-phase system planning rather than as a standalone design decision.
Practical Notes
This equation applies to balanced systems using line values. If the system is significantly unbalanced, phase-by- phase analysis is more appropriate. Power factor also has a strong effect on the final result, so realistic PF values should be used when motors or inductive equipment are involved.
It is also important to keep the units consistent. If the result is easier to read in kilowatts, divide the watt value by 1000. In plant troubleshooting, a quick power estimate from measured line current and voltage can help confirm whether a motor, heater bank, or process load is operating close to the expected demand.