Three-Phase Power Calculator

Three-phase power runs the working world, from factory motors and commercial air conditioning to pumps, compressors, large machinery and the supply to most businesses, and being able to convert between voltage, current and power is a daily task for electricians and engineers. This calculator does it instantly. Enter the line voltage, the line current and the power factor of a balanced three-phase load, and it returns the real power in kilowatts, the apparent power in kilovolt-amps, and the reactive power in kilovolt-amps reactive, all updating as you type. The relationship rests on a single, important factor, the square root of three, which appears because the three phases sit 120 degrees apart, so that real power equals root three times line voltage times line current times power factor. Apparent power uses the same expression without the power factor, and the difference between the two, the reactive power, is the part that flows back and forth without doing useful work. In New Zealand a three-phase supply is typically 400 volts line to line, with 230 volts line to neutral, so the calculator is set up for the line-to-line value that the standard formula uses. Getting these numbers right matters in practice: it lets you size cables, breakers and switchgear, check that a motor or machine sits within the supply available, work out the current a given load will draw, and understand how a poor power factor inflates the current and the apparent power you must provide. It is a reliable everyday tool for electricians, electrical engineers, facilities staff and students learning three-phase theory. The formula and a worked example are set out clearly below.

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