What formula is used for DC circuits?

HP = (I × V × Eff) / 746. Current times voltage gives input watts; multiplied by efficiency gives output watts; divided by 746 converts to horsepower (1 HP = 746 W).

What formula is used for single-phase AC circuits?

HP = (I × V × PF × Eff) / 746. The power factor accounts for the phase difference between voltage and current in AC circuits.

What formula is used for three-phase AC circuits?

HP = (√3 × I × V × PF × Eff) / 746. The √3 factor (≈ 1.7321) accounts for the three-phase relationship. Voltage here is the line-to-line voltage.

What is motor efficiency?

Motor efficiency is the ratio of mechanical output power to electrical input power, expressed as a percentage. Standard motors typically range from 85% to 95% efficient. Higher-efficiency motors waste less energy as heat.

What is the power factor?

Power factor (PF) is a value between 0 and 1 that represents how effectively AC power is converted to useful work. Inductive loads like motors typically have a PF of 0.75 to 0.95. DC circuits have no power factor.

Why is 746 used in the horsepower formula?

One mechanical horsepower is defined as exactly 745.69999... watts, which is conventionally rounded to 746 W. This definition dates to James Watt's comparisons with draft horse output in the 18th century.

Amps to Horsepower Calculator

Convert amperes (A) to horsepower (HP) for DC, single-phase AC, or three-phase AC circuits instantly.

Circuit Parameters

Circuit Type

Current (A)

Voltage (V)

Motor Efficiency (%) (1 – 100)

Power Factor (0 – 1)

Result

Enter values and press Calculate

Formula Reference

DC Circuits

HP = (A × V × Eff) / 746

Single-Phase AC

HP = (A × V × PF × Eff) / 746

Three-Phase AC

HP = (√3 × A × V × PF × Eff) / 746

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Summary

This calculator converts electric current measured in amperes (A) to mechanical output power measured in horsepower (HP). It supports three circuit types: DC, single-phase AC, and three-phase AC. Enter the current, voltage, efficiency, and power factor (for AC circuits) to get the horsepower rating. One mechanical horsepower equals 746 watts.

How it works

Select your circuit type: DC, single-phase AC, or three-phase AC.
Enter the current in amperes (A).
Enter the voltage in volts (V).
Enter the motor efficiency as a percentage (typically 85–95%).
For AC circuits, enter the power factor (between 0 and 1).
The calculator applies the correct formula and displays the result in horsepower (HP).

Use cases

Determine the horsepower output of an electric motor from its nameplate current.
Size replacement motors when the original rating is unknown.
Verify that a motor meets the mechanical load requirements of a machine.
Compare motor efficiency by calculating HP at different operating currents.
Estimate generator output requirements for motor-driven equipment.
Design HVAC systems by converting compressor current to horsepower.
Evaluate pump or fan motor ratings for industrial applications.
Cross-check motor datasheets against measured current draw.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu