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Electric Motor Load & Sizing Calculator

Calculate Full-Load Amps (FLA), torque, and required wire gauge for AC motors. Supports Single/Three-phase systems with NEMA/IEC frame estimation.

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About

Correct sizing of electric motors prevents equipment failure and optimizes energy consumption. Engineers must calculate the Full-Load Amperage (FLA) to size circuit breakers, thermal overloads, and cabling correctly. Under-sizing wiring leads to voltage drops and overheating, while over-sizing increases installation costs unnecessarily.

This tool computes critical operating parameters based on horsepower or kilowatt ratings, voltage, and efficiency class. It accounts for Power Factor (PF) variations which significantly impact the current draw in inductive loads. The calculator also estimates standard NEMA and IEC frame sizes, providing a physical dimension reference for mechanical integration.

motor load FLA calculator electrical engineering NEMA frames IEC motors

Formulas

The Full-Load Current (FLA) for a three-phase motor is calculated using the relationship between power, voltage, and efficiency factors.

For Three-Phase AC:

I = PWV × √3 × PF × η

For Single-Phase AC:

I = PWV × PF × η

Where PW is power in Watts, V is Line-to-Line Voltage, PF is Power Factor, and η is Efficiency (decimal).

Reference Data

Motor Power (HP)Voltage (V) 3φApprox. FLA (A)Min Wire (AWG) @ 75°C
14601.614
54607.614
104601412
204602710
50460654
1004601241
200460240250 kcmil
523015.212

Frequently Asked Questions

Three-phase power delivers energy more consistently. The square root of 3 (approx 1.732) in the denominator of the three-phase formula accounts for the phase offset between the three lines, resulting in lower current for the same power compared to single-phase.
Higher efficiency motors (IE3, IE4) convert electrical energy to mechanical energy with fewer losses. This results in a slightly lower FLA for the same mechanical output power, reducing thermal stress on wiring.
Service Factor (SF) is a multiplier indicating how much a motor can be overloaded for short periods. This calculator determines continuous Full Load Amps (FLA), not the Service Factor Amps (SFA).