Motor Full Load Current Calculator – FLA Amps by HP, Voltage and Phase

Use the free Motor Full-Load Current Estimator below: your data never leaves your browser — all work happens on your device, and nothing is uploaded to any server.

What Full-Load Current Means

Full-load current, usually written FLA, is the current a motor draws when it delivers its rated power at rated voltage. It is the number you need for sizing cables, overload protection, contactors, and starters. It is not the starting current, which can be six times higher for a brief moment, and it is not the no-load current, which is much lower. FLA is the steady working current, and getting it right is the foundation of a safe motor circuit.

This estimator calculates FLA from horsepower, voltage, phase, power factor, and efficiency. It uses the standard relationships: shaft power in watts equals horsepower times 746, single-phase current equals power divided by voltage times power factor times efficiency, and three-phase current divides by the square root of three as well. Those formulas are the same ones in motor textbooks, and they give a solid estimate when the nameplate is missing or unreadable.

How to Use the Estimator

Enter the motor horsepower. If the nameplate gives kilowatts instead, divide by 0.746 to get horsepower, or simply convert in your head: a 3.7 kilowatt motor is about 5 horsepower. Enter the supply voltage, such as 230 volts single-phase or 400 volts three-phase. Choose the phase count, then enter power factor and efficiency. Typical defaults are 0.85 for power factor and 0.90 for efficiency, and the tool uses those as starting values.

The result shows the estimated full-load current, the shaft power in kilowatts, and the apparent power in kVA. The kVA figure is useful for transformer and generator sizing, because those are rated in kVA, not kilowatts. If your motor nameplate lists FLA directly, trust the nameplate over this estimate: the nameplate reflects the actual motor, while the estimator reflects typical values.

A Worked Example

Take a 5 horsepower three-phase motor on 400 volts with 0.85 power factor and 0.90 efficiency. The shaft power is 5 times 746, which is 3,730 watts. The current is 3,730 divided by the square root of three times 400 times 0.85 times 0.90, which is about 7.0 amps. That is the current the cable and overload relay must handle continuously.

Now take a 1 horsepower single-phase motor on 230 volts with the same power factor and efficiency. The shaft power is 746 watts, and the current is 746 divided by 230 times 0.85 times 0.90, which is about 4.2 amps. Notice that the small single-phase motor draws more than half the current of a motor five times its power, because single-phase power has no square-root-of-three factor and the voltage is lower. Voltage and phase matter as much as horsepower.

Why Power Factor and Efficiency Matter

A motor converts electrical energy into shaft work, and both steps lose something. Efficiency accounts for the mechanical and electrical losses inside the motor: a 90 percent efficient motor needs about 11 percent more electrical input than its shaft output. Power factor accounts for the magnetizing current that builds the magnetic field but does no useful work. Together they explain why the supply current is always higher than a naive watts-divided-by-volts calculation suggests.

Small motors tend to have lower power factor and efficiency than large ones, so the defaults of 0.85 and 0.90 are optimistic for a tiny motor and pessimistic for a large premium-efficiency one. If you know the real values from the datasheet, enter them. If you do not, treat the result as an estimate with perhaps 10 to 20 percent uncertainty, and size protection conservatively.

FLA Is Not the Whole Sizing Story

Cable and protection sizing also considers starting current, duty cycle, ambient temperature, and grouping with other cables. A motor that starts under heavy load or starts many times per hour needs a different protection setting than one that starts once a day unloaded. Overload relays are typically set near FLA, while fuses and breakers must tolerate the brief starting surge without tripping. Those settings come from the motor and starter documentation and from local codes, not from this estimator alone.

This estimator is educational only. It estimates steady full-load current from typical formulas, but it does not approve a cable size, a breaker, or an installation. Check your local electrical codes and consult a licensed electrician before doing any electrical work on motors, especially three-phase or industrial equipment.

Frequently Asked Questions

Why is starting current so much higher than FLA? At standstill the motor has no back EMF to limit current, so it briefly draws locked-rotor current, typically five to seven times FLA, until it spins up.

Can I use FLA for a motor run below full load? No, a lightly loaded motor draws less current than FLA, but its power factor also drops. Measure the actual current if you need the part-load value.

What if my motor lists kW, not HP? Divide kilowatts by 0.746 to get horsepower, or remember that 1 horsepower is 746 watts and work from watts directly.

Usa esta herramienta en español