Three-Phase Power Calculator
Calculate active, apparent, and reactive power plus line and phase voltages, currents, and power factor for balanced three-phase loads in star or delta connection.
FreeOnline Tool
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How to Use
The defaults are a star-connected load with 380 V line voltage, 10 A line current, and power factor 0.9.
- Choose the connection: star (Y) or delta (Δ). This changes how phase voltage and phase current relate to the line values.
- Choose what to solve for: three-phase power, line current, or line voltage. When solving for current or voltage, also enter the active power P in kW so the tool can work backward.
- Enter line voltage V_L in volts, line current I_L in amperes, and power factor cosφ. cosφ must be greater than 0 and at most 1.
- Read the results: active power P, apparent power S, reactive power Q, line voltage, line current, power angle φ, phase voltage, phase current, and power factor.
- “Copy result” copies the main values. “Load sample” restores the 380 V, 10 A, cosφ = 0.9 star load.
Features
- Star and delta: in star, phase voltage = line voltage/√3 and phase current = line current; in delta, phase voltage = line voltage and phase current = line current/√3. Both phase values are shown.
- Forward and reverse calculation: compute power from line voltage, line current, and power factor, or solve for line current/voltage when active power is known.
- Complete power results: active P, apparent S, reactive Q, and power angle φ using P = √3·V_L·I_L·cosφ, S = √3·V_L·I_L, and Q = S·sinφ.
- Power-factor validation: cosφ must satisfy 0 < cosφ ≤ 1; invalid values produce a clear message.
- Automatic units: power is shown in W/kW/MW, voltage in V/kV, current in A/kA, and the power angle in degrees with two decimals.
- Local calculation and copy: everything runs in the browser and the main results can be copied at once.
Use Cases
Distribution panel load checks
Use nameplate line voltage, rated current, and power factor to estimate active, apparent, and reactive power for initial breaker and cable selection.
Motor operating point conversion
Given motor input power and line voltage, solve for the running line current and compare it with a clamp-meter reading.
Power-factor correction estimates
Compare reactive power at the current and target power factor to estimate the compensation capacity needed for capacitor sizing.
Teach the √3 relationship
Switch between star and delta to see how phase voltage and phase current change for the same line values.
FAQ
How do star and delta results differ?
Active, apparent, and reactive power plus line voltage and line current are the same. The difference is in phase values: in star, phase voltage is line voltage/√3 and phase current equals line current; in delta, phase voltage equals line voltage and phase current is line current/√3.
Why is active power required when solving for line current or voltage?
From P = √3·V_L·I_L·cosφ, knowing only one of line voltage and line current is not enough to find the other. Solving for current needs voltage and P; solving for voltage needs current and P. P is entered in kW.
What power-factor values are accepted?
cosφ must be greater than 0 and at most 1, such as 0.8, 0.85, 0.9, or 0.95. Zero, negative values, or values above 1 are rejected because the tool models balanced inductive or resistive steady-state loads.
What units are P, S, and Q shown in?
Active power P is in W, apparent power S in VA, and reactive power Q in Var. The tool scales them automatically to W/kW/MW, VA/kVA/MVA, or Var/kVar/MVar.
Does this work for single-phase or unbalanced three-phase loads?
No. It assumes a balanced three-phase steady-state load and ignores harmonics, line impedance, phase imbalance, and neutral current. Use single-phase formulas for single-phase circuits and per-phase analysis for unbalanced loads.