WHP to HP (BHP/Crank HP) Calculator

Enter the wheel horsepower and select the drivetrain of the car to determine the brake HP (crank HP) from WHP.

WHP to HP Calculator

Enter either WHP or engine HP, choose the drivetrain setup, and calculate the missing horsepower along with estimated drivetrain losses.

WHP (Wheel Horsepower)

Drivetrain

Engine HP (BHP / Crank HP)

Drivetrain Loss Table

Drivetrain	Loss	Efficiency	Typical Notes
FWD Manual	10%	0.90	Usually among the lowest drivetrain losses due to a simpler layout and lower parasitic loss.
FWD Automatic	12%	0.88	Slightly higher losses than manual FWD because of the automatic transmission and torque converter effects.
RWD Manual	13%	0.87	Moderate loss from the transmission, driveshaft, and rear differential.
RWD Automatic	15%	0.85	A common rule-of-thumb estimate for many rear-wheel-drive street cars with automatic transmissions.
AWD Manual	18%	0.82	Higher loss because power goes through additional differentials and transfer components.
AWD Automatic	20%	0.80	One of the most common broad estimates used for AWD cars on WHP to crank HP conversions.
4WD Truck / SUV	22%	0.78	Heavier rotating assemblies, larger driveline parts, and truck-oriented systems can raise losses further.
Heavy 4WD / Performance AWD	25%	0.75	Useful as a conservative estimate for very heavy, complex, or high-loss driveline setups.

These are rule-of-thumb estimates, not fixed mechanical constants. Actual drivetrain loss can vary based on transmission type, dyno type, tires, fluids, and vehicle setup.

WHP to HP Formula

The following formula is used to calculate the engine horsepower (hp) from wheel horsepower (WHP).

HP = WHP * 1 / (1 - DL )

Where HP is the engine horsepower
WHP is the wheel horsepower
DL is the drive train loss

To calculate the HP from WHP, multiply the wheel horsepower by 1 divided by the result of 1 minus the drive train loss.

Why are HP and WHP different?

HP is typically used to refer to the true engine horsepower output, while WHP is used to describe the wheel horsepower, which is the horsepower that makes it to the wheel after drive-train loss is accounted for.

How to convert WHP to HP?

Example Problem:

The following example problem outlines the steps and information needed to calculate HP from WHP.

First, determine the wheel horsepower. In this case, the wheel horsepower is measured to be 250 HP.

Next, determine the type of drive train. In this example, we are looking at a front-wheel-drive system.

Next, determine the drive-train loss of the system from the type of drive-train. In this case, the DTL is .10.

Finally, calculate the HP from WHP and DL using the formula above:

HP = WHP * 1 / (1 - DL )

HP = 250 * 1 / (1 - .10 )

HP = 277.77 horsepower

Follow-Up Calculations

If your car makes 300 whp and the drivetrain loss is about 15%, the correction adds back roughly 53 hp, but that same loss can also be expressed as torque at a specific RPM. You can convert that horsepower loss to torque to see whether the drivetrain is eating 40 lb-ft or 70 lb-ft, which is often more useful when comparing transmissions, differentials, and AWD setups.

A result of 300 whp usually becomes about 353 hp at the crank with a 15% drivetrain correction, but that number still assumes sea-level air density. If you live at 5,000 feet, you can estimate power drop in thin air to see how much additional horsepower the engine loses before it ever reaches the wheels.

A car that makes 320 whp at 5,500 rpm is producing about 305 lb-ft at the wheels, because horsepower and torque are tied together by engine speed. After you convert to crank horsepower, the torque at the tires calculation helps you compare launch feel and midrange pull, not just peak dyno numbers.