WHP → HP Calculator
Enter WHP and pick (or set) drivetrain loss. Result updates instantly.
WHP to HP Conversion Guide
Wheel horsepower (WHP) is measured at the wheels on a chassis dyno; engine horsepower (HP) is measured at the crank or flywheel. Because drivetrain components soak up energy through friction and inertia, WHP is always lower than true HP. Typical losses range from about 10 % for front-wheel-drive, 15 % for rear-wheel-drive, and 20 % for all-wheel-drive systems.
WHP to HP – Formula
HP = WHP ÷ (1 − drivetrain loss)
Example
A car showing 275 WHP with an estimated 15 % RWD loss delivers: HP = 275 ÷ 0.85 = 323 hp.
Drivetrain loss reference table:
| Layout | Common loss % | Notes |
| FWD | ≈ 10 % | Shorter driveline, fewer joints |
| RWD | ≈ 15 % | Driveshaft + differential |
| AWD | ≈ 20 % | Extra diffs & transfer case |
How to use the calculator
- Enter your dyno-measured wheel horsepower.
- Select a preset loss or choose “Custom” to enter a specific percentage.
- The true crank horsepower updates instantly.
FAQ
How do I convert HP back to WHP?
Multiply engine horsepower by (1 − loss). Example: 400 hp with a 15 % loss → 400 × 0.85 = 340 WHP.
How accurate are the preset losses?
They’re averages; use a custom percentage if you have precise drivetrain data.
What’s the difference between HP, BHP, CHP and kW?
• HP (horsepower) and BHP (brake horsepower) are both crank figures taken on an engine dyno; “brake” just means the dyno’s brake absorbs the power.
• CHP (crank horsepower) is another synonym—same measurement point.
• kW is the metric unit of power; 1 kW = 1.341 hp. Manufacturers outside North America often quote kW by law.
How do correction factors (SAE, STD, DIN) change WHP?
Dynos “correct” wheel power to a standard temperature, pressure and humidity so numbers are comparable.
• SAE J1349 assumes 77 °F / 29.92 inHg / 0 % humidity and generally gives the lowest numbers.
• STD (older SAE) uses 60 °F and lower barometric pressure, reading 3–5 % higher.
• DIN sits in the middle. Always quote which standard you used.
Can I measure drivetrain loss directly?
A chassis dyno can run a coast-down test: after the pull it lets the rollers spin down in neutral and records the retarding force. Subtracting that curve from the loaded run estimates loss, but tire slip and bearing temperature mean the figure is still an approximation.
Why is the calculator’s default loss 15 %?
It represents an average rear-wheel-drive layout on street tires. Front-wheel-drive drivetrains tend to be shorter (≈ 10 % loss) while all-wheel-drive systems spin additional shafts, transfer cases and differentials (≈ 20 % loss).
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