Motor Current Calculator
Find a motor's full-load current draw from rated power, supply voltage, power factor, and efficiency — for single-phase or three-phase supply.
Enter your values
Motor rating and supply details.
How this calculator works
Full-load current draws on the motor's rated output power, adjusted for the losses (efficiency) and the phase angle between voltage and current (power factor). For a three-phase motor:
For single-phase supply, the √3 term is dropped:
P is rated power in watts, V is line voltage, PF is power factor (0–1), and η is efficiency as a decimal (the calculator converts your % entry automatically).
Typical values for induction motors
| Motor size | Typical PF | Typical efficiency |
|---|---|---|
| Small (<5 kW) | 0.75 – 0.82 | 78 – 85% |
| Medium (5–50 kW) | 0.83 – 0.89 | 86 – 92% |
| Large (>50 kW) | 0.88 – 0.92 | 92 – 96% |
These are general reference ranges — always use the motor's nameplate values when available.
Frequently asked questions
Why is my calculated current different from the nameplate value?
Nameplate current is measured at the motor's actual rated load and test conditions. This calculator gives a close estimate from typical or assumed PF and efficiency figures — use the nameplate current directly whenever it's available.
Should I size cable or breaker from this current directly?
No — full-load current is the starting point only. Cable and protective device sizing must also account for starting current, ambient temperature, grouping, and the applicable electrical code, and should be verified by a qualified electrical engineer.