PhysicsCalcs
Work, Energy & Power

Horsepower Converter

Convert between mechanical hp, metric hp (PS/CV), electrical hp, watts, and kW. Calculate power from torque and RPM or find torque from horsepower.

Interactive calculator

Horsepower Converter

Convert between mechanical hp, metric hp (PS/CV), electrical hp, watts, and kW. Calculate power from torque and RPM, or find torque and RPM from power.

Try an example

1 hp = 550 ft·lbf/s = 745.700 W

Your result will appear here.

Choose a calculation mode, fill in the known values, and click Calculate.

Quick Guide

  • Choose a conversion: hp \u2192 watts, watts \u2192 hp, or torque/RPM.
  • Enter the power or torque value.
  • Click Calculate for all equivalent units.

Table of Contents

Key Takeaways

  • 1 mechanical hp = 550 ft·lbf/s = 745.700 W.
  • 1 metric hp (PS/CV) = 75 kgf·m/s = 735.499 W.
  • 1 electrical hp = 746 W exactly.
  • 1 boiler hp = 9809.5 W (used for steam boilers only).
  • hp = torque[lb·ft] × RPM / 5252.
  • P = τω (watts) where τ is in N·m and ω is in rad/s.
  • Mechanical and electrical hp differ by less than 0.04%.

What Is Horsepower?

Horsepower is a unit of power originally defined by James Watt to compare steam engine output to the work done by draft horses. Today, several different "horsepower" definitions exist, each with a slightly different watt equivalent. The most common are mechanical (Imperial), metric (PS/CV), and electrical horsepower.

Horsepower Definitions (per 1 unit)Mech hp745.7 WMetric (PS)735.5 WElec hp746.0 WBoiler hp9809.5 WScale: bar width proportional to watts (except boiler hp, truncated)

Types of Horsepower

TypeDefinitionWatts
Mechanical (Imperial)550 ft·lbf/s745.700 W
Metric (PS / CV / DK)75 kgf·m/s735.499 W
Electrical746 W (exact)746.000 W
Boiler34.5 lb steam/h @ 212°F9 809.5 W

Quick Conversion Table

FromToMultiply by
hp (mech)kW0.74570
kWhp (mech)1.34102
PSkW0.73550
kWPS1.35962
hp (mech)PS1.01387
PShp (mech)0.98632

HP from Torque & RPM

P=tauomegaqquadhp=fractau[textlb⋅ft]timesRPM5252P = \\tau \\omega \\qquad hp = \\frac{\\tau[\\text{lb·ft}] \\times RPM}{5252}

Power equals torque times angular velocity. In SI units, P (watts) = τ (N·m) × ω (rad/s). In Imperial units, the constant 5252 comes from 33,000 ft·lbf/min ÷ (2π). Torque and horsepower curves cross at 5252 RPM.

How to Use the Calculator

  1. Choose a conversion mode (hp to watts, watts to hp, torque/RPM, etc.).
  2. Enter the known value with units.
  3. Click Calculate.
  4. Review the result in all equivalent units.

Example Calculations

200 hp (mech) to kW

200 × 0.74570 = 149.1 kW

150 PS to hp (mech)

150 × 0.98632 = 147.9 hp

400 N·m @ 3000 RPM

P = 400 × 314.16 = 125 664 W = 168.5 hp

100 kW to all hp

134.1 hp(mech) = 135.96 PS = 134.05 hp(elec)

Typical Engine Power

ApplicationPower
Lawn mower3–7 hp
Economy car80–150 hp
Sports car250–600 hp
Industrial motor (medium)5–50 hp
Diesel locomotive3 000–6 000 hp
Ship engine (container)50 000–100 000 hp

Real-World Applications

IndustryUseHP Type
Automotive (US)Engine ratingsMechanical hp
Automotive (EU/Japan)Engine ratingskW or PS
Electric motorsMotor nameplateElectrical hp or kW
HVACCompressor sizinghp or kW
Marine / steamBoiler capacityBoiler hp

Common Mistakes

  • Confusing mechanical hp with metric hp (PS) — they differ by 1.4%.
  • Using 746 W for all hp types (only correct for electrical hp).
  • Forgetting to convert RPM to rad/s when using P = τω.
  • Confusing BHP (brake horsepower) with WHP (wheel horsepower).
  • Applying the 5252 constant with SI units (it only works with lb·ft and RPM).

Accuracy and Limitations

This converter uses standard definitions. Real-world power measurements depend on testing conditions (SAE net, DIN, JIS standards give different results for the same engine). Drivetrain losses reduce power at the wheels by 10–25% compared to crankshaft power. This tool is educational.

FAQ

What is the difference between mechanical and metric horsepower?›

Mechanical hp (550 ft·lbf/s = 745.7 W) is used in the US and UK. Metric hp or PS (75 kgf·m/s = 735.5 W) is used in Europe, Japan, and most other countries. 1 hp ≈ 1.014 PS.

How do I convert hp to kW?›

Multiply by 0.7457 for mechanical hp, or 0.7355 for metric hp (PS). For example, 200 hp = 149.1 kW.

How do I calculate hp from torque and RPM?›

hp = (torque[lb·ft] × RPM) / 5252. In SI: P(W) = torque(N·m) × ω(rad/s), then divide by 745.7.

What is boiler horsepower?›

1 boiler hp = 9809.5 W. It measures a boiler's capacity to produce steam. It is not directly related to mechanical horsepower.

Why are there different types of horsepower?›

Historical reasons. James Watt defined mechanical hp. Continental Europe adopted the metric system, creating PS. Electrical hp (746 W) was set by convention for motor ratings.

At what RPM do hp and torque curves cross?›

They cross at 5252 RPM (for Imperial units). This is because hp = (torque[lb·ft] × RPM)/5252, so when torque = hp numerically, RPM = 5252.

Is brake horsepower (BHP) different from horsepower?›

BHP is mechanical hp measured at the engine crankshaft (before drivetrain losses). The unit itself (1 BHP = 1 hp = 745.7 W) is the same.

What is PS in car specs?›

PS stands for Pferdestärke (German for horsepower). It is the metric horsepower unit. 1 PS = 0.9863 hp.

Sources

  1. NIST Handbook 44 – Units and Systems of Measurement
  2. SAE International Standards
  3. IEEE Standard Dictionary of Electrical and Electronics Terms
Manish Kumar

Author & technical reviewer

Manish Kumar

PhysicsCalcs tools are reviewed with an educational focus: clear formulas, transparent assumptions, and practical context for students and science learners.

Learn more about Manish