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WHP to HP Calculator

Convert Wheel Horsepower (WHP) to true Engine Horsepower (HP/BHP) and back, using estimated drivetrain losses for FWD, RWD, and AWD vehicles.

whp

WHP ↔ HP Conversion Table (RWD — 15% drivetrain loss)

WHP to HP

WHPHP

HP to WHP

HPWHP

Formulas: HP = WHP ÷ (1 − 0.15) and WHP = HP × (1 − 0.15). Based on RWD 15% drivetrain loss assumption.

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Understanding the WHP to HP Conversion

WHP (Wheel Horsepower) is the power measured at the drive wheels of a vehicle on a chassis dynamometer. HP (Horsepower) — also known as BHP (Brake Horsepower) — is the power measured directly at the engine's crankshaft. The difference between the two is drivetrain loss: the energy consumed by friction in the transmission, driveshaft, differential(s), and axles as power travels from the engine to the wheels.

Car manufacturers advertise crank HP because it's the highest number. When you put your car on a dyno after a tune, the printout gives you WHP. To compare your tuned output to factory specs, you must convert WHP back to estimated crank HP by factoring in drivetrain loss. This calculator lets you do that instantly for FWD, RWD, and AWD vehicles.

WHP to HP Formula

HP = WHP ÷ (1 − DL)
For RWD (15% loss): HP = WHP ÷ 0.85.
Example: 300 WHP ÷ 0.85 ≈ 353 HP.
For AWD (25% loss): 300 ÷ 0.75 = 400 HP.

HP to WHP Formula

WHP = HP × (1 − DL)
For RWD (15% loss): WHP = HP × 0.85.
Example: 400 HP × 0.85 = 340 WHP.
For AWD (25% loss): 400 × 0.75 = 300 WHP.

Drivetrain Loss by Type

FWD (Front-Wheel Drive) loses ~10% — simpler drivetrain with fewer components.

RWD (Rear-Wheel Drive) loses ~15% — longer driveshaft adds friction.

AWD (All-Wheel Drive) loses ~25% — transfer case and extra differentials increase parasitic drag significantly.

What Is a Dynamometer?

A dynamometer (dyno) measures the power output of an engine or drivetrain. A chassis dyno measures WHP by spinning the driven wheels against a roller. An engine dyno measures BHP directly at the crankshaft. The difference between the two readings is the drivetrain loss percentage used in this calculator.

WHP to HP Worked Examples

Example 1 — WHP to HP (RWD): Your RWD car dynos at 320 WHP. Using the formula: HP = 320 ÷ (1 − 0.15) = 320 ÷ 0.85 ≈ 376 HP at the crank.

Example 2 — WHP to HP (AWD): An AWD car shows 400 WHP on the dyno. HP = 400 ÷ (1 − 0.25) = 400 ÷ 0.75 ≈ 533 HP at the crank — AWD cars need significantly more crank power to deliver the same wheel power.

Example 3 — HP to WHP: A manufacturer claims 500 HP for an FWD car. Estimated WHP = 500 × (1 − 0.10) = 500 × 0.90 = 450 WHP. This is what you'd expect to see on a chassis dyno.

Frequently Asked Questions

WHP (Wheel Horsepower) is measured at the driven wheels on a chassis dynamometer. HP (or BHP — Brake Horsepower) is measured at the engine's crankshaft. The difference is drivetrain loss: the energy consumed by friction in the transmission, driveshaft, and differential(s) as power travels from the engine to the wheels.
Divide WHP by (1 minus the drivetrain loss decimal): HP = WHP ÷ (1 − DL). For a rear-wheel drive car with 15% loss: HP = WHP ÷ 0.85. For example, 300 WHP ÷ 0.85 ≈ 353 HP at the crank.
AWD systems include additional mechanical components — a transfer case, front differential, and extra driveshafts — all of which create friction and absorb power. This is why AWD drivetrain loss is estimated at 25%, compared to 15% for RWD and 10% for FWD. An AWD car needs more crank HP to deliver the same WHP as a simpler drivetrain.
In virtually all cases, yes. Because the drivetrain always consumes some energy through friction, WHP is typically 10–25% lower than crank HP. A car rated at 400 HP by the manufacturer might only produce 340–360 WHP on a chassis dyno. If WHP ever reads higher than crank HP, the dyno is likely miscalibrated.
Crank HP is the highest power number available for a vehicle, so it's used for marketing and comparisons. It's also a standardized measurement that's consistent regardless of drivetrain type. WHP varies by drivetrain configuration, making it harder to compare vehicles fairly — though for real-world performance, WHP is more meaningful because it reflects the actual power delivered to the road.
A tune always affects engine output first (crank HP), and that change is then reflected at the wheels (WHP). However, drivetrain upgrades like limited-slip differentials, performance transmission fluids, or lightweight driveshafts can reduce parasitic losses — effectively increasing WHP without changing the engine's crank output. This would show as a smaller gap between HP and WHP.
No — the 10%, 15%, and 25% figures are widely accepted estimates used in the automotive community. Actual drivetrain loss varies by vehicle age, fluid temperatures, component wear, transmission type (manual vs. automatic), and specific differential design. For a precise measurement, you'd need both an engine dyno reading and a chassis dyno reading on the same vehicle under the same conditions.

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