Motor Full Load Current Calculator
Calculate the full-load (running) current of a single-phase, three-phase or DC motor from its nameplate kW or horsepower rating, voltage, power factor and efficiency. Also reports kVA, kVAR, conductor sizing current and typical starting current.
Input
Output
| Metric | Value |
|---|---|
| No data yet | |
Guides
Full-load current (FLC) is the current a motor draws when it is delivering its rated shaft power. It's the number you need before you can size cable, pick an overload relay, or check whether an existing supply can take another machine. This calculator works it out from nameplate data — kW or horsepower, voltage, power factor and efficiency — for single-phase, three-phase and DC motors.
How to use it
- Enter the motor rating and pick its unit. Nameplates outside North America are usually marked in kW; North American ones in horsepower. The rating is the mechanical output at the shaft, not the electrical input.
- Enter the line voltage — line-to-line for a three-phase supply.
- Pick the supply: three-phase, single-phase or DC.
- Set the power factor and efficiency from the nameplate. If they aren't marked, 0.85 and 90% are reasonable starting points for a modern induction motor; small motors run lower on both.
The formulas
- Three-phase: I = Pout / (√3 × V × PF × η)
- Single-phase: I = Pout / (V × PF × η)
- DC: I = Pout / (V × η)
- Electrical input power = Pout / η
- Apparent power (kVA) = input power / PF
- Reactive power (kVAR) = √(kVA² − kW²)
What else it reports
- Conductor sizing current (125% FLC) — continuous-duty motor circuits are conventionally sized at 125% of full-load current so the conductor isn't running at its limit all day.
- Typical DOL starting current (≈6× FLC) — a direct-on-line start briefly pulls several times the running current. Six times is a common rule of thumb for a NEMA Design B / IEC induction motor; the real locked-rotor figure is on the nameplate as a code letter or LRA rating and can be anywhere from about 5× to 8×.
FAQ
Why doesn't my result match the nameplate amps exactly?
Nameplate current is measured on the actual machine, and the power factor and efficiency printed on it are rounded values that both drift with load. A calculated FLC within a few percent of the nameplate figure is normal. Where the two disagree, use the nameplate — this calculator is an estimate for planning, not a substitute for the manufacturer's data.
Does power factor affect the current for a DC motor?
No. Power factor only exists on an AC supply, so the field is hidden when you pick DC, and current is simply output power divided by voltage and efficiency.
Should I size the breaker at 125% too?
No — that figure is for conductor ampacity. Motor branch-circuit short-circuit protection is deliberately set much higher (commonly 250% of FLC for an inverse-time breaker) so the device rides through the starting inrush, with a separate overload device protecting the motor itself. Follow your local wiring regulations for the actual values.
Related tools
To pick a cable for the current this returns, use the Wire Size Calculator. For the mechanical side of the same motor — torque at a given speed — see the Shaft Power & Torque Calculator. For simple voltage/current/resistance relationships, the Ohm's Law Calculator covers those.
Privacy
All calculations run entirely in your browser — nothing you enter is sent to a server.