Three Phase Calculator

How to use the three-phase power calculator

What this calculator does

This calculator estimates the electrical quantities of a balanced three-phase AC load. It converts between line and phase voltage, converts between line and phase current, and calculates apparent power, active power, reactive power, phase angle, and power factor from one consistent set of assumptions. It is useful for checking motor, transformer, heater, feeder, and general industrial-load calculations when all three phases have equal RMS magnitudes and the same phase displacement. It does not model conductor impedance, voltage drop, harmonics, efficiency, starting current, unbalanced phases, or equipment protection settings, so it should not replace an engineered design or field measurement.

When to use it

Use the calculator to translate a motor nameplate's line voltage and line current into kVA and estimated kW, to compare delta and wye phase quantities, to check a measured power factor against the corresponding phase angle, or to prepare a transparent calculation record for a technical worksheet. For background on why three-phase systems use 120-degree phase separation and how delta and wye connections differ, see the three-phase power systems chapter from All About Circuits.

How to calculate

1. The calculator opens with a complete demonstration: Delta connection, 400 V line-to-line, 8.6 A line current, and a 0.84 power factor. The results and a validated Excel workbook are available immediately.
2. Select Connection type. Choose Delta when each phase is connected line-to-line, or Wye / Star when each phase is connected from a line to the neutral point.
3. Select Voltage basis and enter Voltage value. Use line-to-line for a supply measurement between conductors; use phase voltage for the voltage across one load phase.
4. Select Current basis and enter Current value. Use line current for current in a supply conductor; use phase current for current through one branch of the load.
5. Select Power factor input. Enter either the dimensionless power-factor ratio or the phase angle in degrees. Switching modes converts the current value so the electrical state remains the same.
6. Read the live result cards and the detailed table, then select Download Excel to export the current typed model. Reset clears the demonstration and all calculated content; export remains disabled until a complete valid state is entered again.

Input guide

Connection type is required and accepts Delta or Wye / Star. A realistic example is Delta for a 400 V motor. In Delta, phase voltage equals line voltage and line current is √3 times phase current. In Wye, line voltage is √3 times phase voltage and line current equals phase current. The common mistake is mixing a line measurement with a phase formula.

Voltage basis is required and identifies whether Voltage value is line-to-line or phase voltage. Voltage value is a required positive RMS number in volts, entered with a period decimal and optional comma thousands separators; 400 is a typical industrial example. Increasing voltage increases all three power results proportionally when current and power factor stay constant. Do not enter a peak waveform value or use a decimal comma such as 400,5.

Current basis is required and identifies whether Current value is line or phase current. Current value is a required positive RMS number in amperes; 8.6 is the demonstration value. Increasing current increases apparent, active, and reactive power proportionally. A frequent error is using phase current from a delta winding as though it were the larger line current.

Power factor input is required and accepts either Power factor or Phase angle. In Power factor mode, Power factor must be from 0 through 1; 0.84 is the example. In Phase angle mode, Phase angle must be from 0° through 90°; 32.86° is equivalent to 0.84. A higher power factor raises active power for a fixed voltage and current while reducing reactive power. Do not enter 84 for an 84% power factor; enter 0.84.

Output guide

Active power (P) is the estimated useful real power in watts or kilowatts. Apparent power (S) is the voltage-current capacity in VA or kVA. Reactive power (Q) is the quadrature component in var or kvar; NIST notes that the var is the accepted special unit name for reactive power in its SI unit guidance for reactive power. Phase angle (φ) is the angle whose cosine is the power factor. The summary pills repeat the selected connection, current power factor, and whether the identity S² = P² + Q² is numerically consistent.

The table's Phase voltage, Line voltage, Phase current, and Line current rows show the connection conversion. Its Power factor and Phase angle rows show the same displacement in ratio and degree form. The Apparent power, Active power, and Reactive power rows repeat the canonical power outputs and state the relationship used. These are deterministic mathematical estimates for the entered balanced model, not measured equipment performance.

Worked example

With Delta selected, 400 V line voltage, 8.6 A line current, and PF = 0.84, apparent power is √3 × 400 × 8.6 = 5,958.25 VA, displayed as 5.96 kVA. Active power is 5,958.25 × 0.84 = 5,004.93 W, displayed as 5.00 kW. The phase angle is arccos(0.84) = 32.86°, and reactive power is 5,958.25 × sin(32.86°) = 3,232.87 var, displayed as 3.23 kvar. Delta phase voltage remains 400.00 V, while phase current is 8.6 ÷ √3 = 4.97 A. These exact startup values are also written to the initial Excel workbook.