Horsepower Calculator

Calculate horsepower from torque and RPM, calculate torque from HP and RPM, convert between HP, kW, and watts with step-by-step solutions.

Input

Calculate Horsepower

Select a calculation type and enter values to see results with detailed 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 originally defined by James Watt to compare the output of steam engines with the power of draft horses. One horsepower equals 745.7 watts or 0.7457 kilowatts. Horsepower is commonly used to measure the power output of engines, motors, and other mechanical devices.

How to Use This Calculator

  1. Select a calculation type from the dropdown (HP from Torque & RPM, Torque from HP & RPM, RPM from HP & Torque, Convert Power Units, HP from Watts, or HP from Kilowatts).
  2. Enter the required values with appropriate units.
  3. Select your preferred units for torque (ft-lb or N⋅m) and power (HP, kW, or W).
  4. Click 'Calculate' to see the results.
  5. Review the detailed results, visualizations, and step-by-step solution.

Calculation Types

HP from Torque & RPM

Calculate horsepower from torque and RPM using the formula: HP = (Torque × RPM) / 5252. This is the most common calculation for engine power.

Torque from HP & RPM

Calculate torque from horsepower and RPM. Formula: Torque = (HP × 5252) / RPM. Useful for determining engine torque output.

RPM from HP & Torque

Calculate RPM from horsepower and torque. Formula: RPM = (HP × 5252) / Torque. Useful for finding the RPM at which peak power occurs.

Convert Power Units

Convert between horsepower (HP), kilowatts (kW), and watts (W). Supports all common power unit conversions.

HP from Watts

Calculate horsepower from watts. Formula: HP = Watts / 745.7. Useful for converting electrical power to mechanical power.

HP from Kilowatts

Calculate horsepower from kilowatts. Formula: HP = kW × 1.341. Common in European and metric systems.

Key Horsepower Formulas

Horsepower from Torque and RPM:

HP = (Torque × RPM) / 5252

Torque from Horsepower and RPM:

Torque = (HP × 5252) / RPM

RPM from Horsepower and Torque:

RPM = (HP × 5252) / Torque

Power Unit Conversions:

1 HP = 745.7 W = 0.7457 kW

1 kW = 1.341 HP = 1000 W

1 W = 0.001341 HP = 0.001 kW

Torque Unit Conversions:

1 ft-lb = 1.35582 N⋅m

1 N⋅m = 0.737562 ft-lb

Why 5252?

The constant 5252 in the horsepower formula comes from unit conversions. One horsepower is defined as 550 foot-pounds per second. To convert RPM to revolutions per second, we divide by 60. To convert to foot-pounds per minute, we multiply by 60. The calculation: (550 ft-lb/s × 60 s/min) / (2π rad/rev) = 5252. This constant ensures that horsepower and torque curves intersect at 5252 RPM when plotted on the same graph.

Important Notes

  • All torque and power values must be greater than zero.
  • RPM must be between 1 and 50,000 for valid calculations.
  • The formula HP = (Torque × RPM) / 5252 is valid for rotational power calculations.
  • Torque can be entered in foot-pounds (ft-lb) or Newton-meters (N⋅m).
  • Power can be converted between HP, kW, and watts.
  • Results are displayed with step-by-step solutions showing the calculation process.
  • The constant 5252 is specific to the relationship between HP, torque (in ft-lb), and RPM.
  • For metric calculations, torque in N⋅m is automatically converted to ft-lb for the formula.

Common Applications

  • Automotive engine power calculations
  • Motor and engine performance analysis
  • Industrial machinery power ratings
  • Electric motor specifications
  • Power tool performance evaluation
  • Marine and aviation engine calculations
  • Power unit conversions for international standards

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