Free electrical calculators for power work

Three Phase Power Calculator

Enter the line voltage, current and power factor to get three-phase kW, kVA and kvar, or find the current from the power.

The three phase power calculator works out real power, apparent power, reactive power and line current for a three-phase electrical load. Enter the voltage, current or power, and power factor, and it returns the results along with the steps behind them. It runs in your browser, is free, and needs no sign-up. Nothing you enter is uploaded, and every step is shown. Use it for a quick check of a motor, feeder or panel load before you size equipment, or as a 3 phase power calculator for converting between line and phase voltage. Results are for estimation, so verify critical designs against the applicable standard.
Three phase power calculator example

How to use the Three-phase power calculator

  1. Open the Calculate drop-down and choose a mode: Power from voltage and current, Current from power, or Line-to-line and line-to-neutral voltage.
  2. Set Voltage entered is to Line-to-line (V_LL) or Line-to-neutral (V_LN), matching the voltage you measured or read from the nameplate.
  3. Type the voltage in Voltage (V). Typical line-to-line values are 208, 400, 480 and 600 V.
  4. If it appears, type the Line current (I) in amps. This box only shows in some modes.
  5. If it appears, type the Real power (P) and choose its unit: kW, W, MW or hp.
  6. Enter the Power factor (PF). Use 1 for resistive loads and about 0.8 to 0.9 for motors.
  7. Read the result rows. Only the rows that apply to your mode appear. If a warning shows, check the power factor or current value before you rely on the result.
  8. Scroll to How it was calculated to see the formula and each step with your own numbers.

To try a known case first, press one of the example buttons, such as 208 V or 480 V. Copy result copies the result lines and a link. Copy link stores every input in the page address, so the same calculation reopens later. Print / save as PDF produces a file with the inputs, results, steps and date. Reset restores the starting example.

What is the three phase power equation?

Real power in a three-phase circuit is P (W) = √3 × V_LL × I × PF, where V_LL is the line-to-line voltage in volts, I is the line current in amps, and PF is the power factor. Apparent power is S (VA) = √3 × V_LL × I, and reactive power is Q = √(S² − P²).

Current can be found by rearranging the power formula: I = P ÷ (√3 × V_LL × PF). For a balanced load, each phase carries one third of the total power.

As an example, a 480 V line-to-line supply carrying 50 A at a power factor of 0.9 gives 37.41 kW of real power, 41.57 kVA of apparent power and 18.12 kvar of reactive power.

Why is the square root of 3 used in three-phase power?

The square root of 3 (about 1.732) is used because in a three-phase system the line-to-line voltage is √3 times the voltage from one line to neutral. The term converts between the two voltage measurements, so the formula works with the line-to-line value.

The calculator accepts either voltage type. Line-to-line is 208 V for 120 V line-to-neutral, 480 V for 277 V and 400 V for 230 V. A single-phase load connected line-to-line on a three-phase system does not use √3. It uses I = P ÷ (V × PF).

How do you calculate three phase current from power?

Rearrange the 3 phase power equation for current: I = P ÷ (√3 × V_LL × PF). This three phase AC power calculation is what the Current mode does. A 30 kW load at 400 V and PF 0.85 draws 30,000 ÷ (1.732 × 400 × 0.85) ≈ 50.9 A per line. The same 3 phase AC power calculation at 480 V gives about 42.5 A, so a higher supply voltage lowers the current for the same power.

For a quick sense of scale: 208 V × 30 A at PF 1 is 10.8 kW, and 480 V × 100 A at PF 0.9 is 74.8 kW.

Worked examples

InputResult
208 V line-to-line, 30 A, PF 0.99.727 kW, 10.81 kVA
400 V line-to-line, 32 A, PF 0.8518.84 kW, 22.17 kVA
480 V line-to-line, 100 A, PF 0.974.82 kW, 83.14 kVA
230 V line-to-neutral, 16 A, PF 111.04 kW, 11.04 kVA
10 kW, 480 V line-to-line, PF 0.8514.15 A

Calculated by the tool above with these values.

Frequently asked questions

How do you calculate three-phase current?

Divide the real power by √3 × V_LL × PF. For 10 kW at 480 V line-to-line and a power factor of 0.85, the current is 14.15 A.

What is the difference between line and phase voltage?

Line-to-line voltage is measured between two phase conductors. Line-to-neutral voltage is measured between one phase conductor and the neutral. The calculator labels the second value V_LN, and line-to-line equals √3 times line-to-neutral.

How many kW is a 3 phase 100 amp supply?

It depends on the voltage and power factor. At 480 V line-to-line and a power factor of 0.9, a 100 A supply gives 74.82 kW (83.14 kVA). Change either value and the result changes, so enter your own numbers to check.

Can I convert 1 phase to 3 phase with a formula?

No. A formula cannot turn a single-phase supply into a three-phase one. A single-phase load connected line-to-line on a three-phase system is calculated with I = P ÷ (V × PF).

What power factor should I enter?

Use 1 for resistive loads such as heaters and the nameplate power factor for motors. If you enter a value below 0.5, the calculator shows a warning, because that is unusually low for a real load.

Why does the calculator warn about high current?

It warns when the line current is very high. Check the voltage and power first. A higher voltage or parallel feeders may be a better option than a single feeder carrying that current.

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