Three Phase Power Calculator
kW, kVA and current for 3-phase loads.
Reviewed by the Calculation Machine team · Updated 24 October 2026 · How we check our maths
Your values
ⓘ Live results
- Real power
- 18.84 kW
- Apparent power
- 22.17 kVA
- Reactive power
- 11.68 kVAr
- Current per phase
- 32 A
Quick answer
For a balanced three-phase load, real power P (kW) = √3 × line voltage × line current × power factor ÷ 1,000, and apparent power (kVA) is the same without the power factor. A 400 V load drawing 32 A per line at 0.85 power factor uses 18.84 kW and 22.17 kVA.
What the Three Phase Power calculator does
This calculator converts line-to-line voltage, line current and power factor into real power (kW), apparent power (kVA) and reactive power (kVAr) for a balanced three-phase circuit. It covers the same use as a three-phase load calculator for motors, heaters, chillers and distribution boards.
Electricians and engineers use it to check a clamp-meter reading against a motor nameplate, size a supply or generator in kVA, or confirm how much load is on each phase of a panel. Enter the voltage measured between two lines (400 V in the UK and Europe, 208 V or 480 V in North America) and the current in one line.
The figures assume the three phases are balanced — equal current in each line. For unbalanced loads, work out each phase separately (phase voltage × phase current × PF) and add the results.
The formula
S (kVA) = √3 × V_L × I_L ÷ 1,000 P (kW) = S × PF Q (kVAr) = S × sin(arccos PF)
| Symbol | Meaning | Unit |
|---|---|---|
| V_L | Line-to-line voltage | V |
| I_L | Current in each line conductor | A |
| PF | Power factor (cos φ) of the load | 0–1 |
| √3 | ≈ 1.732, the ratio between line and phase voltage in a balanced three-phase system | — |
| S, P, Q | Apparent, real and reactive power | kVA, kW, kVAr |
The formula is the standard balanced three-phase power relation and is the same for star (wye) and delta connections as long as line values are used. To go the other way, I = P × 1,000 ÷ (√3 × V × PF). For motors, nameplate kW or hp is shaft output; divide by efficiency to get electrical input before calculating current. Standard voltages come from IEC 60038 and ANSI C84.1.
Worked examples
European workshop machine at 400 V
A machine on a 400 V supply draws 32 A per line at 0.85 power factor.
Inputs
- Line voltage400 V
- Line current32 A
- Power factor0.85
Result
- Real power18.84 kW
- Apparent power22.17 kVA
- Reactive power11.68 kVAr
- Current per phase32 A
18.84 kW of real power from 22.17 kVA of supply capacity. The 11.68 kVAr of reactive power is what power factor correction would offset.
US industrial feeder at 480 V
A 480 V panel feeding a chiller measures 100 A per line at 0.90 power factor.
Inputs
- Line voltage480 V
- Line current100 A
- Power factor0.9
Result
- Real power74.82 kW
- Apparent power83.14 kVA
- Reactive power36.24 kVAr
- Current per phase100 A
About 75 kW real and 83 kVA apparent. Transformers and generators are rated in kVA, so 83 kVA is the figure to compare against their nameplates.
Commercial kitchen at 208 V
A 208 V three-phase combi oven draws 20 A per line with a near-resistive 0.95 power factor.
Inputs
- Line voltage208 V
- Line current20 A
- Power factor0.95
Result
- Real power6.85 kW
- Apparent power7.21 kVA
- Reactive power2.25 kVAr
- Current per phase20 A
About 6.85 kW. The same 20 A on a 480 V system would deliver 2.3 times the power, which is why large loads are usually supplied at the higher voltage.
Common three-phase voltages by region
Enter the line-to-line figure. The line-to-neutral voltage is the line voltage divided by √3.
| System | Line-to-line | Line-to-neutral | Where used |
|---|---|---|---|
| 400/230 V | 400 V | 230 V | UK, EU, much of Asia, Africa and Australia |
| 208Y/120 V | 208 V | 120 V | US and Canada commercial buildings |
| 480Y/277 V | 480 V | 277 V | US industrial and large commercial |
| 600Y/347 V | 600 V | 347 V | Canada industrial |
| 240 V delta | 240 V | — (or 120 V high-leg) | Older US light industrial |
Converting kW to amps for cable and breaker sizing
Rearranged, the formula gives the current a known load will draw: I = kW × 1,000 ÷ (√3 × V × PF).
- A 30 kW load at 400 V and 0.85 PF draws 30,000 ÷ (1.732 × 400 × 0.85) ≈ 50.9 A per line.
- A motor delivering 15 kW at the shaft with 90% efficiency and 0.85 PF on 480 V draws 15,000 ÷ 0.9 ÷ (1.732 × 480 × 0.85) ≈ 23.6 A.
Cable sizing must also allow for voltage drop on long runs — check it with the wire voltage drop calculator — and for motor starting current, which can be several times running current.
Star and delta: line versus phase values
- Star (wye): line current equals phase current; line voltage = √3 × phase voltage.
- Delta: line voltage equals phase voltage; line current = √3 × phase current.
Because the calculator works with line values, you get the right power for either connection. Mixing a phase voltage with a line current is the most common error and gives an answer 1.732 times too low or too high. To bring a low power factor up, see the power factor correction calculator.
How to use the Three Phase Power Calculator
- 1Enter the line-to-line voltage, measured between any two phases (not phase to neutral).
- 2Enter the current in one line, from a clamp meter or the equipment nameplate; average the three readings if they differ slightly.
- 3Enter the power factor from the nameplate or a power meter; use 1.0 for purely resistive heaters.
- 4Read kW, kVA and kVAr; use kVA to size transformers and generators and kW for energy use.
Frequently asked questions
How do you calculate three-phase power?
Multiply √3 (1.732) by the line voltage, the line current and the power factor. At 400 V, 10 A and PF 1.0 that is 6.93 kW.
How many amps is 10 kW on three-phase?
At 400 V and unity power factor, 10,000 ÷ (1.732 × 400) ≈ 14.4 A per line. At 208 V it is about 27.8 A, and a lower power factor raises the current further.
What is the difference between kW and kVA?
kW is the real power that does work; kVA is the total the supply must carry. They are equal only at a power factor of 1.0.
Why is √3 used in three-phase calculations?
The three voltages are 120° apart, so the voltage between two lines is √3 times the voltage from line to neutral. The factor converts line values into total power.
Is three-phase power more efficient than single-phase?
For the same power, three-phase uses less conductor material and delivers constant rather than pulsing power, which suits large motors. That is why industrial and large commercial loads use it.
References
- IEC 60038: IEC standard voltages — International Electrotechnical Commission (IEC)
- ANSI C84.1: Electric Power Systems and Equipment – Voltage Ratings (60 Hz) — American National Standards Institute (ANSI) / NEMA
- Fundamentals of Electric Circuits, Alexander and Sadiku — McGraw-Hill
About this calculator
- Built and reviewed by the Calculation Machine team · How we build and test calculators
- Last reviewed: October 24, 2026
- Report an error