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Horsepower Calculator

Calculate engine power output from torque and RPM
lb-ft
RPM

Engine Output

Enter torque and RPM values to see the calculated horsepower.

The Ultimate Guide to Horsepower & Torque

What is Horsepower?

Horsepower (HP) is a unit of measurement of power, or the rate at which work is done, usually in reference to the output of engines or motors. The term was adopted in the late 18th century by Scottish engineer James Watt to compare the output of steam engines with the power of draft horses.

In the automotive world, horsepower determines how fast a vehicle can perform work—essentially, how quickly it can accelerate and maintain high speeds.

The Relationship Between Horsepower and Torque

Horsepower and torque are closely related but represent different things. Torque is a measure of rotational force (the "grunt" that gets you moving), while horsepower is a measure of how quickly that force is applied over time.

The Golden Formula:

$$HP = \frac{Torque \times RPM}{5252}$$

This formula is the reason why horsepower and torque curves always cross at exactly 5,252 RPM on a dynamometer graph (when using lb-ft and HP).

How to Use This Calculator

To calculate your engine's horsepower, you need two values:

  1. Torque: The rotational force produced by the engine, measured in pound-feet (lb-ft) or Newton-meters (Nm).
  2. RPM: Revolutions Per Minute, or how fast the engine's crankshaft is spinning.

If you have torque in Newton-meters (Nm), the formula changes slightly to account for the unit conversion:

$$HP = \frac{Torque (Nm) \times RPM}{7127}$$

Brake Horsepower (BHP) vs. Wheel Horsepower (WHP)

It's important to distinguish where the power is being measured:

  • Brake Horsepower (BHP): Measured at the engine's flywheel. This is the number manufacturers usually advertise.
  • Wheel Horsepower (WHP): Measured at the drive wheels. This is always lower than BHP because of "drivetrain loss" (friction in the transmission, driveshaft, and differential), which typically ranges from 10% to 25%.

Different Types of Horsepower

Mechanical Horsepower (hp)

Also known as imperial horsepower. Defined as 550 foot-pounds per second. This is the standard unit used in the US.

Metric Horsepower (PS/cv)

Common in Europe (Pferdestärke). 1 PS is approximately 0.986 mechanical horsepower.

Why Does Horsepower Matter?

Horsepower is a key indicator of a vehicle's performance potential. Higher horsepower generally leads to higher top speeds and better acceleration at high RPMs. However, for daily driving and towing, torque is often more noticeable as it provides the "push" at lower engine speeds.

Frequently Asked Questions

This is a mathematical constant derived from the definition of horsepower. Since $1 HP = 33,000 ft-lb/min$ and the circumference of a 1-foot radius circle is $2\pi$ feet, the constant is $33,000 / 2\pi \approx 5,252$.

Yes, this is common in diesel engines and heavy-duty trucks. They produce massive amounts of rotational force (torque) but operate at low RPMs, resulting in lower total horsepower compared to high-revving sports cars.

Most modern passenger cars have between 150 and 250 horsepower. Compact cars might have around 120-150 HP, while performance cars and large SUVs often exceed 300-400 HP.

Generally, yes. Top speed is limited by the point where the engine's power output equals the aerodynamic drag and rolling resistance of the vehicle. More horsepower allows the car to overcome more drag at higher speeds.

Torque steer is the tendency for some front-wheel-drive cars to pull to one side under heavy acceleration. It happens when the engine's torque is distributed unevenly between the two drive wheels.

Performance Tips

  • Torque gets you moving; HP keeps you moving.
  • Drivetrain loss is usually 15% for RWD/FWD.
  • AWD cars have higher drivetrain loss (20-25%).
  • Peak HP occurs at high RPMs.
  • Peak Torque occurs at lower RPMs.

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Disclaimer

This calculator provides theoretical horsepower based on engine torque and RPM. Actual performance may vary due to environmental conditions, engine health, and drivetrain efficiency.