Utility July 13, 2026 · 8 Min Read

Motor HP Calculator – Guide & Formulas

Solve mechanical horsepower (HP) and torque from rotational speed, and compare against motor electrical draw.

Calculate motor capacity specifications. Input mechanical shaft speed and torque to compute output horsepower, and reference electrical current profiles to estimate operating efficiencies.

Key Takeaway

Use the free Motor HP Calculator to solve mechanical horsepower (hp) and torque from rotational speed, and compare against motor electrical draw. Get instant results with step-by-step explanations.

How to Use the Motor HP Calculator

  1. Input mechanical shaft rotational speed (RPM).
  2. Input shaft output torque rating (in lb-ft).
  3. Input motor operational terminal voltage and current (A).
  4. Review equivalent mechanical horsepower, electrical input energy, and performance factors.

The Formula

Horsepower (HP) = (Torque * RPM) / 5252 | Power (kW) = HP * 0.7457

Variable Definitions

  • T: Rotational shaft torque measured in pound-feet (lb-ft)
  • N: Rotational speed measured in revolutions per minute (RPM)
  • 5252: Mathematical constant matching angular momentum work units to horsepower

Determining Power of a Standard Inductive Motor

Find shaft output horsepower for an electric motor outputting 30 lb-ft of torque at 1,750 RPM.

  1. Step 1: Multiply torque by rotational speed: 30 × 1,750 = 52,500.
  2. Step 2: Divide by the work constant: 52,500 / 5,252 ≈ 9.996 HP.
  3. Step 3: Convert output to kilowatts: 9.996 × 0.7457 ≈ 7.45 kW.
  4. Step 4: This represents a standard nominal 10-horsepower industrial electric motor.

Frequently Asked Questions

What is the physical relationship between speed and torque?

For a given horsepower, speed and torque are inversely proportional. Gearing down a motor decreases RPM while proportionally multiplying output torque.

Why is the number 5252 used in the formula?

It represents the ratio of 33,000 foot-pounds per minute (one horsepower) to 2π radians per revolution (one full rotation), converting angular speed to linear power.