HP to Amps Calculator

Converting Horsepower to Amps

Motor nameplates list horsepower, but wire sizing, breakers, and contactors need current in amps. This calculator converts mechanical horsepower to electrical input current using voltage, motor efficiency, and (for AC) power factor.

Formulas

DC motor:

$$I = \frac{HP \times 746}{V \times \eta}$$

AC single-phase motor:

$$I = \frac{HP \times 746}{V \times PF \times \eta}$$

One horsepower equals 746 watts. $V$ is line voltage, $\eta$ is efficiency (as a decimal), and $PF$ is power factor.

Practical Notes

Efficiency accounts for electrical losses inside the motor. Power factor reflects how much of the apparent power does real work in AC circuits. Use nameplate values when available. For branch circuit design, consult local electrical codes and add appropriate safety margins.

Frequently Asked Questions

Why use 746 watts per horsepower?

746 W is the standard conversion between mechanical horsepower and electrical watts in US motor calculations.

What efficiency should I enter?

Typical motor efficiencies range from 80% to 95%. Use the motor nameplate or manufacturer data when possible.

When is power factor needed?

For AC motors. DC circuits have power factor of 1. Induction motors often run between 0.8 and 0.95 power factor.

Is this the same as full-load current?

It estimates input current at rated horsepower. Starting (inrush) current can be several times higher for a short period.

Can I size wire with this result alone?

Use this as a starting point. Final wire and breaker sizing must follow applicable electrical codes and installation conditions.

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Converting Horsepower to Amps

Formulas

Practical Notes

Frequently Asked Questions

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