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Three-Phase Motor Full-Load Amperage Calculator

Estimate a three-phase motor's full-load current draw from its horsepower, voltage, and efficiency.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Estimated full-load amperage

11.73 A

Check your inputs

This is a calculated estimate — for actual motor circuit conductor and overcurrent protection sizing, NEC 430.250 REQUIRES using the tabulated FLA values from NEC Table 430.250, not the motor nameplate current or a calculated value, per code.

Running these inputs gives 11.7 as the estimated full-load amperage. Note that motor horsepower (hp) sits at the low end of the range this calculator was checked against, so treat the output as indicative rather than settled. Expect some drift against the real job; the calculation is solid but conditions on site are not. Currently reading for United States under IRC 2024 — pick a different market above and the figures re-cast accordingly.

Add the equipment this sizes

This result is a specification — 11.729 A — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Standard three-phase motor FLA formula: FLA = (HP × 746) ÷ (√3 × voltage × efficiency × power factor), derived from the electrical power relationship P = √3 × V × I × PF applied to motor output power converted to input electrical power via efficiency

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Frequently asked questions

How is three-phase motor full-load amperage calculated?
FLA = (HP × 746) ÷ (√3 × voltage × efficiency × power factor). This converts the motor's rated mechanical output power (horsepower, converted to watts) into the electrical input current drawn at the given line-to-line voltage, efficiency, and power factor.
Can I use this calculated value to size conductors or breakers?
No — this is a calculated estimate only. For actual motor circuit conductor and overcurrent protection sizing, NEC 430.250 REQUIRES using the tabulated FLA values from NEC Table 430.250, not the motor nameplate current or a calculated value, per code.
Why do efficiency and power factor both appear in the formula?
Efficiency accounts for losses converting electrical input power to mechanical output power, while power factor accounts for the phase difference between voltage and current in an AC circuit — both are needed to relate the motor's rated horsepower output back to its actual electrical current draw.