Skip to main content

Three-Phase Power Calculator — kW, kVA, kVAR + Line Current

P = √3 · VL · IL · cosφ — active kW, apparent kVA, reactive kVAR and reverse line current — browser-only

  • Runs locally
  • Category Calculator
  • Best for Getting a realistic range before a purchase, plan, workout, or schedule decision.

Enter line voltage, line current and power factor for active kW, apparent kVA and reactive kVAR. Switch to reverse to size a feeder from a known power.

Quick loads
Line current IL (A)
Line voltage VL (V)
Power factor cosφ
Result
Active power P
5.5426 kW
Apparent power S
6.9282 kVA
Reactive power Q
4.1569 kVAR
Line current IL
10 A
P = √3 · VL · IL · cosφ · S = √3 · VL · IL · √3 ≈ 1.732

Values are LINE quantities (between two lines), not phase values. In a star supply VL = √3 · Vphase.

What this tool does

Free three-phase power calculator for balanced industrial loads. Enter the line voltage VL, line current IL and power factor cosφ and read active power P in watts and kilowatts, apparent power S in kVA and reactive power Q in kVAR. The working formula is P = √3 · VL · IL · cosφ, where √3 is about 1.732 and the voltages and currents are line values, not phase values. Flip into reverse mode to size a feeder: give the kW a motor draws plus its voltage and power factor and the tool returns the line current IL = P ÷ (√3 · VL · cosφ), the number you need to pick a breaker and cable. A power factor of 1 makes P equal S, a lagging 0.8 motor pulls more current for the same kilowatts. Everything runs in your browser with one-click copy and a shareable URL that reopens your exact numbers. 100% client-side, no upload.

Tool details

Input
Files + Numbers
The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output
Live result + Copy
The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy
Browser-side processing
The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share
Shareable URL state
Key settings are encoded in the URL so another person can reopen the same setup.
Performance budget
Initial JS <= 9 KB
No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit
Calculator · Developer
Category and role tags drive related tools, internal links, and quick fit checks.

How to use

  1. 1. Input

    Paste or drop your content into the tool panel.

  2. 2. Process

    Click the button. All processing is local in your browser.

  3. 3. Copy / Download

    Copy the result or download to disk in one click.

How Three-Phase Power Calculator fits into your work

Use it for fast estimates, comparisons, and planning numbers before you make the final call.

Calculation jobs

  • Getting a realistic range before a purchase, plan, workout, or schedule decision.
  • Comparing scenarios by changing one input at a time.
  • Turning rough assumptions into a number you can discuss.

Calculation checks

  • Double-check units, dates, rates, and rounding assumptions.
  • Treat health, finance, tax, and legal outputs as planning aids, not professional advice.
  • Save the inputs that produced an important result so you can reproduce it later.

Good next steps

These links move the current task into a more complete workflow.

  1. 1 Ohm's Law Calculator Enter any two of voltage, current, resistance, or power — get the other two plus the formula used — with mV/V/kV, µA/mA/A, Ω/kΩ/MΩ, mW/W/kW prefixes — browser-only. Open
  2. 2 Voltage Drop Calculator Wire and cable voltage drop from current, run length, conductor size and material, with the 3% limit check, copper vs aluminium, single-phase and three-phase, browser-only Open
  3. 3 Scientific Calculator Scientific calculator — sin / cos / log / sqrt / power, with full keyboard input + history, deg/rad mode. Open

Real-world use cases

  • Size a breaker and cable for a three-phase motor

    A workshop adds a 7.5 kW lathe on a 400 V supply with a nameplate power factor of 0.85. Switch to reverse mode, type 7.5 kW, 400 V and 0.85, and the tool returns about 12.7 A per line. Now you know to pick a 16 A breaker with margin and a cable rated above 12.7 A, before you buy anything. No more guessing the current from the kilowatts in your head and over-spending on copper.

  • Check whether a feeder is overloaded

    A panel meter reads 415 V and 28 A on a balanced load. Enter those line values at a measured power factor of 0.9 and read S ≈ 20.1 kVA and P ≈ 18.1 kW. Compare that against the feeder rating and the transformer kVA to see how much headroom is left before the next machine goes on. The shareable URL lets you send the snapshot to the duty electrician.

  • Convert a motor nameplate kW into running amps

    Nameplates list kW and power factor but the breaker is rated in amps. Drop the plate values in reverse mode and the line current falls out of IL = P ÷ (√3 · VL · cosφ). A 11 kW pump at 400 V and 0.86 pulls about 18.5 A. Keep a tab open per motor and the URLs become a tidy current schedule you can paste into a commissioning sheet.

  • Teach the power triangle in a trades class

    Show apprentices why a 0.8 power factor matters: hold VL and IL fixed and watch P drop while S stays put as you lower cosφ. The kW, kVA and kVAR readouts make the right-triangle relationship concrete instead of abstract, and the √3 factor stops being a mystery once they see 6928 W versus the wrong 4000 W for the same 400 V and 10 A.

Common pitfalls

  • Dropping the √3. Multiplying VL · IL · cosφ without the 1.732 factor undercounts three-phase power by 42 percent. A 400 V, 10 A, unity load is 6928 W, not 4000 W. The √3 only disappears for single-phase, never for a balanced three-phase line.

  • Mixing line and phase values. The formula here wants line voltage and line current, the figures on the nameplate and meter. Feeding it the 230 V phase voltage of a 400 V star supply by mistake throws every result off by a factor of √3.

  • Forgetting the power-factor units when reversing. In reverse mode the power must be in the same unit you selected, watts or kilowatts. Typing 7.5 while the field says watts asks for 7.5 W and returns a tiny current instead of the 7.5 kW motor you meant.

Privacy

Every calculation — the √3 power formula, the kVA and kVAR figures and the reverse line current — is plain JavaScript that runs in your browser tab. No voltage, current or motor rating ever leaves the page, and nothing you type is logged. The one caveat: the shareable URL encodes your inputs in the query string, so a "share link" pasted into chat records those numbers in the recipient server's access log. For a sensitive site survey, use the copy button and paste the text rather than sharing the URL.

FAQ

Tool combos

Folks in your role tend to reach for these alongside this tool.

Browse all tools for this role
Made by Toolora · 100% client-side · Updated 2026-05-30