What formula is used to convert torque to horsepower?

The standard mechanical formula is HP = Torque (lb-ft) × RPM / 5252. The constant 5252 comes from converting the definition of horsepower (33,000 ft-lb/min) through 2π radians per revolution. For metric units, kW = Torque (Nm) × RPM / 9549.

Why do HP and torque curves always cross at 5252 RPM?

At exactly 5252 RPM, the formula HP = Torque × RPM / 5252 equals HP = Torque numerically, so the curves must intersect. Below 5252 RPM torque exceeds HP; above it HP exceeds torque.

How do I convert lb-ft to Nm?

Multiply lb-ft by 1.35582 to get Nm. For example, 300 lb-ft equals 406.7 Nm. This tool performs that conversion automatically when you switch units.

What is the difference between HP and kW?

1 mechanical horsepower equals 0.7457 kilowatts. So 100 HP ≈ 74.6 kW. kW is the SI standard used in most countries outside the United States.

Can I use this for electric motors?

Yes. The formula HP = Torque × RPM / 5252 applies to any rotating machine. Electric motors often produce peak torque from 0 RPM, so entering the motor's continuous torque and operating RPM gives a valid power estimate.

What does the reverse conversion do?

Reverse mode solves for torque given power and RPM: Torque (lb-ft) = HP × 5252 / RPM. This is useful when you know a target horsepower and need to figure out what torque the engine must produce at a specific RPM.

Torque to HP Calculator

Name: Torque to HP Calculator
Availability: InStock
Author: Nham Vu

Enter torque and RPM to get HP and kW instantly — supports lb-ft and Nm inputs and reverse HP-to-torque conversion.

Standard dyno formula: HP = Torque (lb-ft) × RPM / 5252

Torque unit:

Torque (lb-ft)

RPM

Formula Reference

Imperial (lb-ft)

HP = Torque × RPM / 5252

Metric (Nm)

kW = Torque × RPM / 9549

Conversions: 1 lb-ft = 1.35582 Nm • 1 HP = 0.7457 kW

Summary

Enter torque and RPM to get HP and kW instantly — supports lb-ft and Nm inputs and reverse HP-to-torque conversion.

How it works

Choose a conversion direction: Torque + RPM to Power, or Power + RPM to Torque.
Select your preferred torque unit (lb-ft or Nm).
Enter the torque (or power) value and the engine RPM.
Horsepower and kilowatts (or torque in both units) are calculated instantly.
Use the formula reference card at the bottom to understand the math.

Use cases

Convert dyno sheet torque readings to peak horsepower.
Verify manufacturer torque and HP specs against the standard formula.
Compare European Nm specs with American lb-ft and HP figures.
Calculate required torque at a given RPM to hit a target horsepower.
Cross-check engine tuning results across different unit systems.
Quickly convert between HP and kW for international spec sheets.

Frequently Asked Questions

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Last updated: 2026-05-29 · Reviewed by Nham Vu