Key Takeaways
- BHP: Measured at the crankshaft before drivetrain losses
- WHP: Measured at the wheels after drivetrain losses
- HP: Generic horsepower measurement (often gross HP)
- Drivetrain Loss: 15-25% depending on FWD/RWD/AWD
Complete Guide to Horsepower Measurements
The BHP to HP Calculator helps you understand and convert between different horsepower measurements used in the automotive industry. Whether you're shopping for a vehicle, modifying your car, or analyzing dyno results, understanding these power measurements is essential.
The Evolution of Horsepower Measurement
Horsepower has been measured in various ways throughout automotive history, leading to different standards and measurement methods:
Gross Horsepower (Pre-1972)
Measured without accessories, alternator, or exhaust restrictions
Net Horsepower (SAE J1349)
Modern standard with all accessories installed
DIN Horsepower
European standard similar to SAE net
JIS Horsepower
Japanese Industrial Standard
Understanding Drivetrain Power Losses
When power travels from the engine to the wheels, some energy is lost through friction and mechanical inefficiencies in the drivetrain components:
2-5% power loss depending on type (manual vs automatic)
1-2% additional loss in RWD/AWD vehicles
3-5% power loss through gear friction
1-3% loss from mechanical friction
How to Use This Calculator
Converting between BHP, HP, and WHP is straightforward:
Real-World Applications
Compare manufacturer BHP claims with real-world dyno WHP figures
Calculate expected power gains from modifications
Understand the relationship between crank and wheel power
Calculate power-to-weight ratios and class eligibility
SAE Standards and Industry Compliance
The Society of Automotive Engineers (SAE) maintains standards for power measurement. SAE J1349 is the current standard for net power measurement, ensuring consistent and comparable ratings across manufacturers.