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CalcChef

Brake Horsepower Calculator

Calculate brake horsepower from torque and RPM, convert the result to kW, and optionally estimate wheel horsepower and power-to-weight ratio. How it works

Use the Brake Horsepower Calculator

Brake Horsepower (BHP)
300.0 hp
Power 223.7 kW

300 lb-ft × 5252 RPM ÷ 5252 = 300.0 hp

About the Brake Horsepower Calculator

400 Nm of torque at 5,000 RPM is 280.9 brake horsepower, or 209.4 kW. In lb-ft the rule is bhp = torque × RPM ÷ 5,252, so 300 lb-ft at 6,000 RPM is 342.7 hp. Torque in newton-meters is converted to lb-ft first, which makes the Nm constant 7,120.8.

Brake horsepower and kW for common torque and RPM pairs

TorqueRPMBrake horsepowerkW
100 lb-ft3,00057.1 hp42.6 kW
250 lb-ft5,500261.8 hp195.2 kW
300 lb-ft5,252300.0 hp223.7 kW
300 lb-ft6,000342.7 hp255.6 kW
400 lb-ft6,500495.0 hp369.2 kW
200 Nm7,000196.6 hp146.6 kW
400 Nm5,000280.9 hp209.4 kW
500 Nm4,000280.9 hp209.4 kW

Torque × RPM is what sets the power, so 400 Nm at 5,000 RPM and 500 Nm at 4,000 RPM give the same figure.

Supported inputs

  • Torque in lb-ft or Nm
  • Engine speed in RPM
  • Optional drivetrain loss percentage
  • Optional vehicle weight in pounds or kilograms

Supported outputs

  • Brake horsepower (mechanical hp)
  • Power in kilowatts (kW)
  • Optional wheel horsepower after the entered drivetrain loss
  • Optional horsepower per 1,000 lb of vehicle weight, with a kilogram weight converted to pounds

Methodology

bhp = torque (lb-ft) × RPM ÷ 5,252, where 5,252 = 33,000 ÷ 2π. Torque in Nm is divided by 1.3558 to get lb-ft, so the Nm constant is 5,252 × 1.3558 = 7,120.8. kW = bhp × 0.7457. Wheel hp = bhp × (1 − loss ÷ 100). Power-to-weight = bhp ÷ weight in lb × 1,000, with kilograms multiplied by 2.20462 first.

Assumptions

  • Torque and RPM must describe the same operating point; peak torque and peak RPM from different points cannot produce a meaningful peak-power result.
  • The wheel-horsepower estimate treats drivetrain loss as a simple percentage and is not a dynamometer measurement.

How to use this tool

  1. Enter the torque and choose lb-ft or Nm.
  2. Enter the engine speed in RPM at which that torque was measured.
  3. Optionally add a drivetrain loss percentage for an estimated wheel horsepower, and the vehicle weight for horsepower per 1,000 lb.

Frequently asked questions

How do you convert torque and RPM to horsepower?
Multiply torque in lb-ft by RPM and divide by 5,252. 250 lb-ft at 5,500 RPM is 261.8 hp. For Nm, divide the torque by 1.3558 first, or divide torque × RPM by 7,120.8: 200 Nm at 7,000 RPM is 196.6 hp.
Why are torque and horsepower equal at 5,252 RPM?
Because 5,252 is the constant in the formula: one horsepower is 33,000 ft·lb per minute, and one revolution turns through 2π radians, so 33,000 ÷ 2π = 5,252. At that speed torque × RPM ÷ 5,252 equals the torque, which is why 300 lb-ft at 5,252 RPM is 300.0 hp. In Nm the two figures do not cross at 5,252.
What is the difference between hp, PS and kW?
This calculator gives mechanical horsepower, 745.7 W, which is why kW = hp × 0.7457. Metric horsepower (PS), common on European spec sheets, is 735.5 W, so 280.9 hp is about 284.8 PS and 209.4 kW.
Is BHP the same as wheel horsepower?
No. Brake horsepower is measured with a load (brake) dynamometer before drivetrain losses, usually at the crankshaft. A chassis dyno measures at the wheels, which reads lower. The wheel figure here is only bhp × (1 − the loss you enter); the tool has no built-in loss for any gearbox or drive layout.
Does the power-to-weight figure work in kilograms?
The result is always horsepower per 1,000 lb. A weight in kg is converted to pounds first, so 342.7 hp in a 1,500 kg car shows 103.6 hp per 1,000 lb. For hp per tonne, divide the hp by the mass in tonnes yourself: 342.7 ÷ 1.5 = 228.5.

Reading power off a torque curve

A dyno sheet or a maker's spec gives torque at a stated RPM, and the horsepower at that point follows from the two numbers. Take both from the same point on the curve: an engine with 300 lb-ft at 4,000 RPM makes 228.5 hp there, and pairing that torque with a 6,000 RPM redline gives 342.7 hp, a figure the engine only reaches if it still makes 300 lb-ft at 6,000.

Peak horsepower usually sits above the torque peak, because power keeps rising with RPM while torque falls off slowly. To find it, run the calculator at several points along the curve and take the largest result. A chassis dyno reads at the wheels; enter a drivetrain loss only to estimate a wheel figure from a crank figure, and treat the percentage as your own assumption.

bhp = torque × RPM ÷ 5,252

bhp = torque (lb-ft) × RPM ÷ 5252

One mechanical horsepower is 550 ft·lb per second, or 33,000 ft·lb per minute, and one revolution is 2π radians, so 33,000 ÷ 2π = 5,252. That is also why torque in lb-ft and horsepower are equal at 5,252 RPM.

Torque in Nm is divided by 1.3558 to get lb-ft, which makes the Nm constant 5,252 × 1.3558 = 7120.8: 400 Nm at 5,000 RPM is 280.9 hp.

kW = bhp × 0.7457, because a mechanical horsepower is 745.7 W. Wheel horsepower is bhp × (1 − loss ÷ 100) with the loss you enter. Power-to-weight is bhp ÷ weight in lb × 1000; a weight in kg is multiplied by 2.20462 first, so the result is always hp per 1,000 lb.

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