Brake Horsepower (BHP) Calculator
Calculate your engine's raw power output using torque and RPM or Wheel Horsepower (WHP).
What is Brake Horsepower (BHP)?
Brake Horsepower (BHP) measures the amount of power an engine generates before any power is lost to auxiliary components such as the gearbox, alternator, differential, and water pump. It is essentially the "raw" power of the engine measured at the crankshaft.
The term "Brake" comes from the original method used to measure power: using a brake (decelerator) to apply a load to the engine and measuring the force required to keep the engine at a specific speed.
How to Calculate BHP from Torque
The relationship between torque, RPM, and horsepower is mathematical. In the imperial system (lb-ft and HP), the formula is:
BHP = (Torque × RPM) / 5252
Why 5252? This is the constant that balances the units of measurement. Interestingly, on a dyno graph, torque and horsepower curves always cross at exactly 5,252 RPM.
Estimating BHP from Wheel Horsepower (WHP)
When a car is tested on a chassis dynamometer (rolling road), the result is Wheel Horsepower. To estimate the engine's BHP, you must account for "drivetrain loss." This is the energy lost through friction and heat in the transmission and axles.
| Drive Layout | Typical Loss (%) |
|---|---|
| Front-Wheel Drive (Manual) | 10% – 13% |
| Rear-Wheel Drive (Manual) | 13% – 15% |
| Automatic Transmission | 18% – 22% |
| All-Wheel Drive (AWD) | 20% – 25% |
Real-World Calculation Example
If your engine produces 350 lb-ft of torque at 6,000 RPM, the calculation would be:
- 350 × 6,000 = 2,100,000
- 2,100,000 / 5,252 = 399.8 BHP
If you dyno your car and get 300 WHP on a Rear-Wheel Drive manual car (15% loss), the BHP estimate would be:
- 300 / (1 – 0.15) = 352.9 BHP