Wheel Horsepower Calculator
Estimate wheel horsepower from crank horsepower and drivetrain loss, or reverse the calculation
Estimated horsepower
How we calculated it
About the Wheel Horsepower Calculator
Wheel horsepower is the power measured or estimated at the driven wheels after drivetrain losses, while engine or crank horsepower is measured before those losses. Comparing the two can help estimate drivetrain loss or translate a dyno result.
A single drivetrain-loss percentage is only an approximation. Losses vary with transmission type, speed, temperature, tire behaviour and dyno method, and the relationship is not always a perfectly fixed percentage.
How to Use the Wheel Horsepower Calculator
- Enter crank horsepower and an assumed drivetrain-loss percentage, or enter wheel horsepower if solving in the opposite direction.
- Choose the calculation direction.
- Calculate estimated wheel or crank power.
- Treat the result as an estimate unless both values come from comparable measured conditions.
How the Calculation Works
Estimated wheel horsepower = crank horsepower × (1−loss fraction).
If wheel horsepower and loss fraction are known, estimated crank horsepower = wheel horsepower ÷ (1−loss fraction). The reverse calculation should divide rather than simply add the loss percentage back.
Worked example
Wheel Horsepower Calculator Worked Example
400 hp crank power with 15% assumed loss
Wheel horsepower = 400×0.85 = 340 whp.
Result guide
Understanding Your Wheel Horsepower Calculator Result
The estimate represents power after the assumed drivetrain loss. Adding 15% to 340 whp would give 391 hp, not 400 hp, which shows why the reverse calculation must divide by the retained fraction.
Before you rely on the answer
Assumptions and Limitations
- Loss percentage is an approximation appropriate to the scenario.
- Crank and wheel power use comparable correction standards.
- Accessory and dyno-method differences are outside the simple loss model.
Practical tip
Using This Result in Practice
Compare dyno results only when correction method, gear, tire setup and test conditions are similar. A precise-looking wheel horsepower number can move significantly between different dynamometers.
Related calculations
Useful Calculations to Continue With
If you need to calculate mechanical horsepower from torque and RPM, use the Horsepower Calculator.
If the power value needs conversion between horsepower and kilowatts, use the Power Converter.
Common questions
Wheel Horsepower Calculator FAQ
What is wheel horsepower?
Power measured or estimated at the driven wheels after drivetrain losses.
How do I estimate WHP from crank HP?
Multiply crank horsepower by one minus the assumed drivetrain-loss fraction.
Can I add the loss percentage to WHP to get crank HP?
Not exactly. The reverse calculation divides by the fraction of power retained.