WHP to HP Calculator
Convert wheel horsepower to engine (crank) horsepower using drivetrain loss.
A chassis dyno measures wheel horsepower (WHP), but engine specs are quoted in crank horsepower. This calculator converts your dyno's wheel figure back to crank power by adding the drivetrain loss.
WHP to HP Formula
How to Use This Calculator
- Enter wheel horsepower from your dyno sheet.
- Set drivetrain loss % for your layout.
- Read estimated crank horsepower.
Worked Example
For the opposite direction, see the wheel horsepower calculator, and read wheel HP vs crank HP for the full explanation.
Why You Divide Instead of Adding the Loss Back
If a drivetrain loses 15%, the wheels receive 85% of crank power — so to recover crank HP you divide WHP by 0.85, not multiply by 1.15. Dividing 300 WHP by 0.85 gives 353 crank HP, whereas wrongly adding 15% gives only 345. The gap widens as losses rise, so using the correct operation matters for an honest power claim.
Drivetrain Loss by Layout
Loss grows with the number of components between engine and tires. Front-wheel drive is the most direct (~10–12%), rear-wheel drive sits in the middle (~15–17%), and all-wheel drive loses the most (~20–25%) because it drives two axles. Manual gearboxes are generally a touch more efficient than automatics. These are conventions, not exact constants — the same car can read differently on different dynos.
Crank HP from 300 WHP by Loss
| Drivetrain | Loss | Crank HP |
|---|---|---|
| FWD | 12% | 341 |
| RWD | 15% | 353 |
| AWD | 22% | 385 |
WHP to Crank HP Conversion Chart
Quick lookup using typical drivetrain losses — 12% FWD, 15% RWD, 20% AWD. Divide wheel HP by (1 − loss):
| WHP | Crank HP (FWD, 12%) | Crank HP (RWD, 15%) | Crank HP (AWD, 20%) |
|---|---|---|---|
| 200 | 227 | 235 | 250 |
| 250 | 284 | 294 | 313 |
| 300 | 341 | 353 | 375 |
| 400 | 455 | 471 | 500 |
| 500 | 568 | 588 | 625 |
| 700 | 795 | 824 | 875 |
| 1000 | 1136 | 1176 | 1250 |
These are planning figures — real loss varies with transmission type, tire pressure and dyno type. Manual gearboxes lose less than the old torque-converter automatics that spawned the 15–20% folklore.
Frequently Asked Questions
Divide wheel horsepower by (1 minus the drivetrain loss fraction). For 15% loss, divide by 0.85.
Roughly 10% for FWD, 15% for RWD, and 20–25% for AWD. Automatics tend to lose a little more than manuals.
The drivetrain absorbs power through friction before it reaches the wheels, so the crank figure is always higher than what the dyno reads at the wheels.
It's an approximation. Real losses vary with transmission type, temperature, and even tire and roller friction on the dyno.
Crank (flywheel) horsepower, measured on an engine dyno before drivetrain losses.