What formula is used for DC motors?

HP = (V × I × Eff) / 746. Voltage multiplied by current 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 motors?

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

What formula is used for three-phase AC motors?

HP = (√3 × V × I × 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 and why does it matter?

Motor efficiency is the ratio of mechanical output power to electrical input power, expressed as a decimal or percentage. Standard motors typically range from 85% to 95% efficient. A lower efficiency means more electrical energy is wasted as heat.

What is a typical power factor for AC motors?

Inductive loads like motors typically have a power factor between 0.75 and 0.95. Unity PF (1.0) would mean all supplied power is converted to useful work, which is only possible in purely resistive circuits.

Why is 746 used in the horsepower formula?

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

What is the difference between electrical and mechanical horsepower?

Mechanical horsepower (1 HP = 746 W) is used for motor output ratings. Electrical horsepower (1 HP ≈ 746 W) is the same value. Boiler horsepower (1 HP = 9,809.5 W) is a different unit used for steam boilers and should not be confused.

Volts to Horsepower Calculator

Enter voltage, current, and efficiency to convert volts to horsepower for DC, single-phase AC, or three-phase AC motors.

Motor Parameters

Circuit Type

Voltage (V)

Current (A)

Motor Efficiency (%) (1 – 100)

Result

Enter values and press Calculate

Formula Reference

DC Circuits

HP = (V × I × Eff) / 746

Single-Phase AC

HP = (V × I × PF × Eff) / 746

Three-Phase AC

HP = (√3 × V × I × PF × Eff) / 746

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Summary

This calculator converts electrical voltage (volts) combined with current (amperes) and motor efficiency into mechanical output power measured in horsepower (HP). It supports three circuit types: DC, single-phase AC, and three-phase AC. Enter the voltage, current, efficiency, and power factor (for AC circuits) to instantly compute horsepower. One mechanical horsepower equals 746 watts.

How it works

Select your circuit type: DC, single-phase AC, or three-phase AC.
Enter the voltage in volts (V).
Enter the current in amperes (A).
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 voltage.
Size replacement motors when only voltage and current ratings are known.
Verify a motor meets the mechanical load requirements for industrial equipment.
Compare motor efficiency by calculating HP at different supply voltages.
Estimate generator capacity requirements for motor-driven machinery.
Design HVAC systems by converting compressor voltage and current to horsepower.
Evaluate pump or fan motor ratings from electrical specifications.
Cross-check motor datasheets against measured voltage and current draw.

Frequently Asked Questions

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