Horsepower Calculator
Calculate horsepower from torque and engine RPM, or estimate horsepower from quarter-mile elapsed time and trap speed.
How to use the Horsepower Calculator
- Enter your inputs into the Horsepower Calculator above.
- Results update instantly as you type — no submit button needed.
- Adjust any value to see how the result changes in real time.
The horsepower formulas
HP = (Torque × RPM) / 5252 · · · From quarter-mile: HP ≈ Weight × (Speed/234)³
Torque is in lb-ft, RPM in revolutions per minute, weight in lb, speed in MPH. The 5,252 constant comes from converting work and time units. Quarter-mile estimate uses Roger Huntington's formula.
Worked example
A car producing 350 lb-ft of torque at 4,500 RPM: HP = (350 × 4,500)/5,252 ≈ 300 hp. A 3,500 lb car running a quarter mile at 120 MPH: HP ≈ 3,500 × (120/234)³ ≈ 472 hp at the wheels.
Frequently asked questions
Why does horsepower = torque at 5,252 RPM?
Because of the constant in the formula — at exactly 5,252 RPM, the HP and lb-ft numbers always equal each other. Useful for diagnosing dyno graph errors.
What's the difference between HP and brake HP?
Brake horsepower (bhp) is measured at the crankshaft. Wheel HP (whp or RWHP) is measured at the drive wheels — typically 10–20% lower due to drivetrain losses.
Is horsepower the same as torque?
Different things. Torque is rotational force; horsepower is the rate of doing work. High torque feels strong off the line; high horsepower wins at high speed.