Motor FLA Calculator
This motor FLA calculator finds the full-load amps of an electric motor from its horsepower, voltage, efficiency, and power factor. Enter the values and the motor FLA calculator returns the full-load current for single-phase, three-phase, or DC motors, so you can size cables, breakers, and overloads to the current the motor draws at its rated load.
Results
The Motor FLA Calculator is part of our AC & Three Phase collection. Browse more ac & three phase to size, convert, and check your work alongside this tool.
What the motor FLA calculator does
FLA stands for full-load amps, the current a motor draws when it is working at its rated output. This motor FLA calculator derives that current from the motor horsepower, the supply voltage, the efficiency, and the power factor. As an fla electrical calculator it accounts for the losses inside the motor, so the full load amps figure reflects the real input current, not just the ideal output power.
The motor FLA calculator method
The motor FLA calculator starts from the output power and works back to the input current. One horsepower is 746 watts, so the input power is that divided by the efficiency, and the current follows from the voltage and power factor:
For single phase the √3 drops out, and for DC the power factor drops out too. The motor full load current is higher than a simple power-over-voltage estimate because the efficiency and power factor account for the losses a real motor has.
Motor FLA calculator example
A 10 HP three-phase motor on 400 V with 90% efficiency and 0.85 power factor. The full load amps calculation:
So the motor draws about 14 A at full load. Enter your nameplate values and the motor FLA calculator returns the full-load current for your motor.
How to use the motor FLA calculator
Choose the phase, then enter the motor power in horsepower, the supply voltage, the efficiency, and the power factor from the nameplate. The motor FLA calculator converts the horsepower to watts, divides by the efficiency to find the input power, and returns the full-load current. Using the nameplate values gives an fla calculation that matches the motor rated current closely.
Reading the motor FLA calculator result
The full-load amps is the steady current at rated load, and it is the basis for sizing the circuit. Cables and overloads are picked from the FLA, while the breaker must also tolerate the much larger starting current, often several times the FLA, without tripping. Always compare the motor FLA calculator result to the nameplate FLA if one is printed, since the nameplate value governs; use the calculation when the plate is missing or you are planning before purchase.
When to use the motor FLA calculator
- Sizing cable and overloads from the full load amps calculator result
- Estimating motor full load current before a motor is bought
- Checking a nameplate FLA with an fla electrical calculator
- Planning a circuit when the nameplate is missing
Common motor FLA calculator mistakes
- Ignoring efficiency and power factor. Leaving them out underestimates the motor full load current.
- Sizing the breaker on FLA alone. The breaker must ride through starting current, several times the full load amps.
- Overriding the nameplate. When a nameplate FLA is printed, it governs over the fla calculation.
Tips for accurate results
- Use the nameplate efficiency and power factor in the motor FLA calculator.
- Size overloads around the FLA and the breaker for the starting surge.
- Prefer the printed nameplate FLA when it is available.
Why the fla electrical calculator divides by efficiency
A simple estimate divides output power by voltage, but the motor FLA calculator goes further because a real motor is not perfect. Some of the electrical input is lost as heat in the windings and core, so the input power is larger than the mechanical output; dividing by the efficiency captures that. Then power factor enters, because an AC motor draws current partly out of step with the voltage, so more current flows than the real power alone implies. Both effects push the full load amps above the naive figure, which is exactly why an fla electrical calculator that ignores them will undersize a circuit. Using the nameplate efficiency and power factor gives an fla calculation you can trust.
The fla electrical calculator versus starting current
The FLA is the steady running current, but a motor pulls far more at the instant it starts, often five to seven times the full load amps, as it overcomes inertia. This matters for how you protect the circuit: the overload relay is set around the FLA to protect the motor windings, while the breaker or fuse must be large enough to ride through the starting surge without tripping yet still clear a fault. The motor FLA calculator gives the running figure that anchors both decisions, and pairing it with the motor starting factor and local code turns the number into a safe circuit design.
Motor FLA calculator chart
Approximate full-load amps of a three-phase motor at 400 V, 90% efficiency, 0.85 power factor, from the motor FLA calculator:
| Motor power | Full-load amps |
|---|---|
| 1 HP | 1.4 A |
| 5 HP | 7.0 A |
| 10 HP | 14.1 A |
| 20 HP | 28.2 A |
| 50 HP | 70.4 A |
Motor FLA Calculator FAQ
What is motor FLA?
FLA is full-load amps, the current a motor draws at its rated output. The motor FLA calculator finds it from horsepower, voltage, efficiency, and power factor.
How is the full load amps calculated?
Convert horsepower to watts, divide by efficiency for the input power, then divide by voltage and power factor (and √3 for three phase). The motor FLA calculator does this fla calculation for you.
Why is FLA higher than power over voltage?
Because a real motor has losses. Dividing by efficiency and power factor raises the current above the ideal figure, giving the true motor full load current.
Should I use the nameplate FLA or the calculation?
Use the nameplate FLA when it is printed, since it governs. Use the fla electrical calculator when the plate is missing or you are planning before purchase.