Three phase power calculator
Convert between power, current, voltage and power factor.
Try a job 5
Each job fills in example values. Replace them with your values.
- Convert amps to three phase powerThe kW and kVA of a 63 A three phase load at 400 V.
- Find kW from a clamp readingThe kW of 100 A at 0.8 power factor.
- Find the kVA of a single‑phase loadThe kVA of 40 A at 230 V.
- Find the reactive power of a loadThe kvar of 50 A at 0.7 power factor.
- Turn a meter reading into kWThe kW from a metered current and power factor.
Inputs
A worked example with the default inputs.
- Phases
- Three phase
- Voltage
- 400 V
- Current
- 50 A
- Power factor
- 0.9
Apparent power
34.64kVA
- Real power
- 31.18kW
- Reactive power
- 15.1kvar
This result is a design aid. Verify it against the current standard.
Calculation steps
- Apparent powerResult34.64kVA
- Real power31.18kW
- Reactive power15.1kvar
About this calculator
How this is calculated
The tool converts between current, apparent power, real power and reactive power. It works on one phase or on three. It does not read a standard. The method is the power triangle.
- Inputs. You pick one phase or three. You enter the voltage, the current and the power factor. On three phases the voltage is the line voltage.
- Apparent power. On three phases, S = √3 × V × I ÷ 1000. On one phase, S = V × I ÷ 1000. The result is in kVA.
- Real power. P = S × power factor. The result is in kW.
- Reactive power. Q = √(S² − P²). The result is in kvar.
Enter the line voltage on three phases, such as 400 V. Enter the phase voltage on one phase, such as 230 V.
Worked example
- 50 A at 400 V on three phases, power factor 0.9. The apparent power is 34.64 kVA. The real power is 31.18 kW. The reactive power is 15.1 kvar.
Limits
The tool assumes a balanced load. It assumes a sine wave. A load with harmonics needs a true RMS reading. The tool does not size a cable or a device. Use the cable size calculator for that. A motor has efficiency as well as power factor. Use the motor tool for its full load current.
Use the tool to check a meter reading, a motor plate or a supply request. For a load in kW, the full load current tool works the other way. A low power factor raises the kVA for the same kW. The power factor correction tool finds the capacitor size.
See also: kVA to amps at 400 V, Current and power factor to kW and Power factor and reactive power.
Questions
The result is a design aid. Verify against the current standard.
What does the three phase power calculator do?
The tool converts a voltage, a current and a power factor into apparent power, real power and reactive power. It works on one phase or on three phases. The three phase result uses the square root of three and the line voltage.
Which inputs matter most?
Voltage and current set the apparent power. The power factor splits that apparent power into real power and reactive power. A power factor of 1 gives no reactive power. On three phases, enter the line to line voltage, not the phase to neutral voltage.
What are the common gotchas?
The tool works out the reactive power from the magnitudes. It therefore does not show whether the load is leading or lagging. The result assumes the three phases carry equal, balanced loads. The inputs sit in the page address, so a link reproduces the same conversion.
Worked examples
- Ohm's law on a 3 kW water heater elementWork the current and working resistance of a 3 kW, 230 V water heater element with Ohm's law, why a cold meter reading is lower, then a 9 kW three‑phase bank.
- Three‑phase power: kVA to amps at 400 VThe root three relation between amps, kVA and kW on a 400 V board, worked at 50 A and a 0.9 power factor, with the kvar figure the engine returns.
Background
- Ohm's law and power on d.c. and a.c.Ohm's law and the power formulas on d.c., single‑phase and three‑phase a.c.: how power factor and impedance change them, and how any two values give the rest.
- Maximum demand and diversityWhy consumer mains are smaller than the sum of the loads. The four methods of Cl 2.2.2, the Table C1 groups, and a house that lands on 70.18 A.
- Power factor and reactive powerWhat power factor is, why a low one costs current and capacity, how a capacitor bank corrects it in steps, and when harmonics call for a detuned bank.
- Harmonics and neutral sizingWhy third harmonic current adds in the neutral of a four‑wire circuit, what the 0.86 factor does, and how to apply it by hand to a cable size result.
Related tools
- Neutral current of an unbalanced loadThe neutral current of an unbalanced three‑phase load.AS/NZS 3000
- Full load current calculatorCalculate full load current from power, voltage and phase.No standard
- Cable size calculatorFind the smallest cable size that passes each check.AS/NZS 3008.1.2AS/NZS 3008.1.1AS/NZS 3000
Was this useful?
A question, or a value that looks wrong? Contact us.