Engine Power/Torque Converter (HP ↔ kW ↔ Nm)

Engine Power / Torque Converter

HP · PS · kW · Nm · lb-ft · kgf-m · torque–power–RPM

Convert Power

Convert Torque

Fill exactly TWO of the three and leave one blank — the blank one is solved using P = T × ω. Torque and power cannot be linked without RPM.

Result

Convert power across mechanical HP, metric PS and kW (correct distinct definitions), torque across Nm, lb-ft and kgf-m, or solve the torque-power-RPM relationship by leaving any one of the three blank

Mechanical (imperial) horsepower, metric PS/CV and kW are three different definitions — 1 HP = 745.7 W, 1 PS = 735.5 W — so a "100 hp" car and a "100 PS" car are not identical; this tool keeps them distinct and labels each. The torque-power-RPM relationship is exact for the instantaneous values at that RPM, but a real engine's peak power and peak torque occur at different RPM points on its dyno curve, so a single conversion is one point, not the whole curve. The 5252 (HP/lb-ft) and 9549 (kW/Nm) constants are just 33000/2π and 60000/2π — the same physics in different units, which is why power and torque curves always cross at 5252 rpm on an HP/lb-ft chart.

Engine Power/Torque Converter: HP, PS, kW, Nm, lb-ft, kgf-m and the Torque-Power-RPM Solver

Mechanical horsepower, metric PS and kW are three genuinely different definitions of power, not interchangeable labels for the same number, so a “300 hp” spec and a “300 PS” spec are not the same engine. this hp to kw converter and horsepower calculator uses the correct distinct constant for each, 745.7 W for mechanical HP, 735.5 W for metric PS and labels which one it means at every step, rather than quietly treating them as identical. Its core feature is the torque to hp calculator relationship solver, give any two of power, torque and RPM, in whichever units you have them, and it finds the third using the exact physics P = T×ω, the same relationship behind the familiar HP = torque×RPM/5252 and kW = torque×RPM/9549 shortcuts. A custom RPM field accepts any dyno-chart point, redline or idle speed, since torque and power genuinely cannot be interconverted without knowing the RPM they were measured at.

How to Use

This tool has two tabs: Unit Convert and Torque · Power · RPM.

Step 1: Using Unit Convert mode
  • Under Convert Power, enter your Power Value and select its Unit: Mechanical HP, Metric PS (CV) or kW. Tap Convert Power to see it converted into all three units at once.
  • Under Convert Torque, enter your Torque Value and select its Unit: Nm, lb-ft, or kgf-m. Tap Convert Torque to see it converted into all three units at once.
Step 2: Using the Torque · Power · RPM relationship solver
  • Switch to the Torque · Power · RPM tab.
  • Fill in exactly two of the three fields, Power (with its unit, Mechanical HP, Metric PS or kW), Torque (with its unit, Nm, lb-ft, or kgf-m) and RPM, any value at all, a specific dyno-chart point, redline or idle speed, and leave the third field blank.
  • Tap Solve Relationship. The tool calculates the value you left blank using the exact physics relationship P = T × ω, showing the result across all relevant units.
Step 3: Exporting your result
  • Use Print / PDF for a clean printable copy or Copy to paste the figures elsewhere.

Key Features

  • Correct, distinct power unit definitions, mechanical HP (745.7 W), metric PS (735.5 W) and kW, never quietly treated as interchangeable
  • Torque conversion across Nm, lb-ft, and kgf-m, all three shown together
  • Torque-Power-RPM relationship solver, the core feature, leave any one of the three blank and the tool solves it from the other two using exact SI physics
  • Custom RPM field, accepting any value, not just a fixed reference speed, so you can check a specific dyno point, redline, or idle
  • Clear explanation of the 5252 and 9549 constants and why HP and torque curves always cross at exactly 5252 RPM on an imperial dyno chart
  • Export as PDF or copy the result.

Formula / Logic Used

Power Unit Constants

1 Mechanical HP=745.699872 W,1 Metric PS=735.49875 W1\ Mechanical\ HP = 745.699872\ W, \qquad 1\ Metric\ PS = 735.49875\ W

Torque Unit Constants

1 lb-ft=1.35581794833 Nm,1 kgf-m=9.80665 Nm1\ lb\text{-}ft = 1.35581794833\ Nm, \qquad 1\ kgf\text{-}m = 9.80665\ Nm

The Core Relationship: Power = Torque × Angular Velocity

P=T×ω=T (Nm)×2π×RPM60P = T \times \omega = T\ (Nm) \times \frac{2\pi \times RPM}{60}

This exact SI relationship is what the familiar shortcuts actually come from:

HP=T (lb–ft)×RPM5252,kW=T (Nm)×RPM9549HP = \frac{T\ (lb\text{-}ft) \times RPM}{5252}, \qquad kW = \frac{T\ (Nm) \times RPM}{9549}

Where 5252 = 33,000 ÷ 2π and 9549 = 60,000 ÷ 2π, both derived directly from the SI relationship above, just expressed in different units. This is also exactly why horsepower and torque curves always cross at 5252 RPM on an imperial (lb-ft/HP) dyno chart, at that specific RPM, the two numbers become numerically equal by definition, not because of anything about the engine itself.

Who Should Use This Tool

Automotive engineering students and enthusiasts comparing engine specifications across regions that use different unit conventions, US HP, European PS or SI kW. also useful for anyone reading a dyno chart who needs to convert a torque and RPM reading into power or vice versa, at a specific point on the curve.

Frequently Asked Questions (FAQs)

1. Is 100 HP the same as 100 PS?

No, mechanical HP equals 745.7 watts while metric PS equals 735.5 watts, a difference of about 1.4%, so 100 HP is slightly more power than 100 PS. This tool always keeps the two distinct and clearly labelled rather than treating them as interchangeable.

2. How do I convert torque and RPM into horsepower?

Use the relationship P = T × ω, which in familiar shortcut form is HP = torque(lb-ft) × RPM ÷ 5252 or kW = torque(Nm) × RPM ÷ 9549. This tool’s relationship solver does this instantly and works in reverse to find torque or RPM too if those are your two known values instead.

3. Why do horsepower and torque curves cross at exactly 5252 RPM on a dyno chart?

The constant 5252 comes directly from the definition of horsepower (33,000 ft-lb per minute divided by 2π), so at precisely 5252 RPM, the numerical value of torque in lb-ft becomes mathematically equal to horsepower. It’s a unit artifact of the conversion constant, not a special property of any particular engine.

4. Can I find the RPM if I know both torque and power?

Yes, since the relationship links all three quantities together, entering torque and power while leaving RPM blank lets this tool’s solver work backward to find the RPM at which those torque and power values would occur together.

5. Why does a diesel engine with more torque sometimes have less horsepower than a sportbike engine?

Because power depends on both torque and RPM together, a high-torque diesel engine running at low RPM and a low-torque sportbike engine running at very high RPM can produce the same or even different horsepower figures despite very different torque numbers. This tool’s relationship solver shows exactly how torque, power and RPM interact for any specific combination.

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