Automotive Calculator
WHP to HP Calculator
Convert wheel horsepower (WHP) to crank horsepower (HP) and back with drivetrain loss presets for FWD, RWD, and AWD. Use custom loss percentages when you have dyno data or platform-specific experience.
WHP to HP Calculator
Convert wheel horsepower to crank horsepower
Results
Enter values and click Calculate
Pro Tuning Notes from the Shop
After more than a decade in automotive performance tuning, the most common mistake I see is comparing dyno numbers without accounting for drivetrain loss. A clean conversion keeps your build plan honest, especially when you are stacking upgrades like turbos, cams, and fuel system changes.
Use the presets for quick estimates, and switch to a custom loss percent if you have baseline dyno data for your exact drivetrain. That is the fastest way to keep your numbers realistic and your parts list on budget.
WHP and HP Conversion Formulas
This calculator uses standard drivetrain loss formulas:
Example Calculations
Quick reference examples using common drivetrain loss values.
Example 1 - WHP to HP (RWD)
WHP 350, drivetrain loss 18% (RWD)
HP = 350 / (1 - 0.18) = 426.83 HP
Power Loss = 426.83 - 350 = 76.83 HP
Example 2 - HP to WHP (FWD)
HP 500, drivetrain loss 15% (custom)
WHP = 500 x (1 - 0.15) = 425 WHP
Power Loss = 500 - 425 = 75 HP
Example 3 - Loss Percentage
HP 450, WHP 380
Loss % = (450 - 380) / 450 x 100 = 15.56%
What Changes Drivetrain Loss
- Transmission type: Automatics and dual-clutch setups often show higher losses than lightweight manuals.
- Differentials and axles: Heavier driveline parts and multiple differentials add drag and inertia.
- Dyno setup: Tire pressure, strapping force, and correction factors can shift WHP numbers by several percent.
- Tire and wheel mass: Heavier wheels increase rotational mass and can reduce measured WHP.
Frequently Asked Questions
- What is the difference between WHP and HP?
- Wheel horsepower (WHP) is measured at the wheels on a dyno and reflects drivetrain losses. Crank horsepower (HP or BHP) is measured at the engine and is always higher. The gap is the power lost through the transmission, differential, and driveline.
- What drivetrain loss percentage should I use?
- Typical losses are about 12% for FWD, 18% for RWD, and 22% for AWD/4WD. Performance drivetrains or heavy duty setups can run higher. Use custom loss if you have dyno data or shop experience with a specific platform.
- Why does my WHP to HP conversion vary between dynos?
- Different dyno types (inertia vs load), correction factors, tire pressure, and drivetrain temperature can change WHP results. This calculator gives a clean estimate based on loss percent, but real-world testing will vary.
- Is this calculator accurate for tuned cars?
- It is accurate for estimating crank output when you know the drivetrain loss. For tuned cars with upgraded transmissions or differentials, use a custom loss value based on your build or dyno baseline.