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Horsepower Calculator

Quick Conversions

100 HP74.57 kW
100 kW134.1 HP
300 lb-ft @ 5252300 HP
400 Nm @ 5252295 HP

Power Equivalents

1 HP (mechanical)745.7 W
1 HP (metric)735.5 W
1 kW1.341 HP
1 HP550 ft-lb/s

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Understanding Horsepower

What is Horsepower?

Horsepower is a unit of power invented by James Watt to compare steam engine output to the work done by draft horses. One mechanical horsepower equals the power needed to lift 550 pounds one foot in one second, or 33,000 foot-pounds per minute.

HP from Torque Formula

HP = (Torque x RPM) / 5252
Where torque is in lb-ft and 5252 is a constant derived from unit conversions

Types of Horsepower

TypeDefinitionWatts
Mechanical HPImperial/US standard745.7 W
Metric HP (PS)European standard (Pferdestarke)735.5 W
Electric HPUsed for electric motors746 W
Boiler HPSteam boiler capacity9,810 W
Hydraulic HPFluid power systems745.7 W

Power vs Work vs Torque

Power (HP/Watts)

  • Rate of doing work
  • Work per unit time
  • Determines speed capability
  • P = Work / Time

Work (Joules)

  • Force x Distance
  • Energy transferred
  • Measured in joules
  • W = F x d

Torque (lb-ft/Nm)

  • Rotational force
  • Twisting strength
  • Force x Lever arm
  • T = F x r

Common HP Applications

Vehicles

  • Lawnmower: 3-20 HP
  • Motorcycle: 15-200 HP
  • Economy Car: 100-150 HP
  • Sports Car: 300-700 HP

Equipment

  • HVAC Compressor: 1-5 HP
  • Workshop Tool: 0.5-3 HP
  • Industrial Pump: 5-100 HP
  • Ship Engine: 10,000-80,000 HP

The 5252 Constant

The number 5252 comes from the relationship between HP, torque, and RPM. It is derived from: 33,000 ft-lb/min (definition of 1 HP) / (2 x pi) = 5252.11. At exactly 5252 RPM, HP and torque values are always equal.

Frequently Asked Questions

How do I calculate horsepower from torque?

Use the formula: HP = (Torque x RPM) / 5,252. Torque is measured in lb-ft. For example, an engine producing 300 lb-ft at 4,500 RPM makes: (300 x 4,500) / 5,252 = 257 HP.

Why is 5,252 used in the horsepower formula?

The constant 5,252 comes from the definition of horsepower (33,000 ft-lb/min) divided by 2π. At exactly 5,252 RPM, horsepower and torque values are always equal. Above this RPM, HP exceeds torque; below it, torque exceeds HP.

What is the difference between HP and kW?

Both measure power but use different scales. 1 mechanical horsepower equals 745.7 watts (0.746 kW). 1 kilowatt equals 1.341 HP. European cars often list power in kW or metric HP (PS), which is slightly different at 735.5 watts.

What is brake horsepower (BHP)?

Brake horsepower measures engine output at the flywheel using a dynamometer (brake). It represents the power available before drivetrain losses. Wheel horsepower (WHP) is typically 15-20% lower due to transmission and differential losses.