Horsepower Calculator

Calculate horsepower from torque and RPM, find torque from HP, or convert between HP, kW, and watts. Free, fast, and easy to use.

Calculate

Choose a calculation type, enter your values, and click Calculate Now to get instant results with step-by-step solutions.

Complete User Guide

What is Horsepower?

Horsepower (HP) is a unit of power that measures the rate at which work is done. It was defined by James Watt to compare steam engines with draft horses. One mechanical horsepower equals 745.7 watts or 0.7457 kilowatts. Horsepower is the standard power rating for car engines, electric motors, and industrial machinery worldwide.

All Formulas at a Glance

HP from Torque: HP = (Torque × RPM) / 5252

Torque from HP: Torque = (HP × 5252) / RPM

RPM from HP: RPM = (HP × 5252) / Torque

Conversions: 1 HP = 745.7 W = 0.7457 kW

4 Calculation Types

HP from Torque & RPM

The most common engine power calculation. Enter torque (ft-lb or N·m) and RPM.

Torque from HP & RPM

Find how much torque an engine produces at a given HP and RPM.

RPM from HP & Torque

Find the RPM at which an engine produces peak power for a given torque.

Convert Power Units

Convert between horsepower (HP), kilowatts (kW), and watts (W).

How to Use This Calculator

  1. Pick a calculation type — HP from torque, torque from HP, RPM from HP, or power conversion.
  2. Enter torque in foot-pounds (ft-lb) or Newton-meters (N·m) as needed.
  3. Enter RPM or horsepower depending on the mode.
  4. Click Calculate Now and see instant results with step-by-step breakdown and chart.

Why 5252?

The constant 5252 comes from unit conversions. One horsepower is 550 ft-lb per second. To go from RPM to radians per minute: (550 × 60) / (2π) ≈ 5252. This means horsepower and torque curves always cross at 5252 RPM when plotted on the same graph.

Key Conversion Factors

• 1 HP = 745.7 Watts = 0.7457 kW

• 1 kW = 1.341 HP = 1,000 Watts

• 1 ft-lb = 1.3558 N·m

• 1 N·m = 0.7376 ft-lb

Quick Examples

• 300 ft-lb at 5252 RPM → (300 × 5252) / 5252 = 300 HP

• 200 HP at 6000 RPM → (200 × 5252) / 6000 = 175.07 ft-lb

• 150 HP = 111.86 kW = 111,855 W

Important Notes

  • All torque and power values must be greater than zero.
  • HP = (Torque × RPM) / 5252 applies only to rotational power in imperial units.
  • Newton-meter inputs are automatically converted to ft-lb for the formula.
  • These are mechanical (brake) horsepower values. Other HP definitions exist (metric HP, electrical HP).

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