Horsepower & Wheel HP Calculator (BHP, WHP, kW)

Calculate engine flywheel horsepower (BHP), chassis wheel horsepower (WHP), kilowatts (kW), and quarter-mile power using SAE formulas and drivetrain loss analysis.

Calculation Method

Live calculation
Quick Vehicle Presets
lb-ft
RPM
lbs
Flywheel Brake Horsepower (BHP)
366.5 HPvia HP = (Torque × RPM) ÷ 5,252
Chassis Dyno Output300.6 WHP

Kilowatts (kW)

273.3 kW

Metric PS / CV

371.6 PS

Power Density

209.4 HP/ton

Weight-to-Power

9.5 lbs/HP

Drivetrain Power Transfer Breakdown

FWD (~12% Loss)

322.5 WHP

RWD (~18% Loss)

300.6 WHP

AWD (~24% Loss)

278.6 WHP

With RWD (~18% Drivetrain Loss), this powertrain produces 300.6 WHP at the wheels from 366.5 BHP at the crankshaft.

Equivalent to 273.3 kW or 371.6 metric PS.

Engineering Principles of Horsepower & Mechanical Power Delivery

In automotive engineering, horsepower ($HP$) quantifies the rate at which torque is exerted across time. While torque represents instantaneous rotational twisting force, horsepower determines a vehicle's sustained acceleration and top-end terminal velocity.

Horsepower & Drivetrain Governing Formulas
1. SAE Flywheel Horsepower (BHP)
HP =
Torque (lb-ft) × RPM5,252

Torque in lb-ft at given crankshaft speed

2. Chassis Wheel HP (WHP)
WHP = BHP × (1 - Loss%)

FWD: ~12% | RWD: ~18% | AWD: ~24%

3. Quarter-Mile ET Estimation
HP =
Weight (lbs)(ET ÷ 5.825)³

Empirical drag strip kinematic model

Standard Power Unit Equivalents
1 HP = 0.7457 kW|1 kW = 1.3410 HP|1 HP = 1.0139 PS (Metric CV)|1 lb-ft = 1.3558 N·m
Step-by-Step Calculation Breakdown
Example 1: Naturally Aspirated V8 (350 lb-ft Torque at 5,500 RPM)
1. Parameters: Torque T = 350.00 lb-ft, Engine speed RPM = 5,500 RPM
2. Calculate Flywheel HP: HP = (350 × 5500) ÷ 5252 = 1,925,000 ÷ 5252 = 366.53 BHP
3. Apply RWD 18% drivetrain loss: WHP = 366.53 × (1 - 0.18) = 300.55 WHP
4. Metric conversion: 366.53 × 0.7457 = 273.32 kW (371.61 PS)
Example 2: 3,500 lb Drag Car Running 12.0s Quarter-Mile
1. Parameters: Curb weight W = 3,500 lbs, Quarter-mile time ET = 12.00 s
2. Compute denominator: (12.00 ÷ 5.825)³ = (2.0601)³ = 8.7431
3. Compute estimated power: HP = 3500 ÷ 8.7431 = 400.31 HP

Vehicle Performance Classes & Power Benchmarks

Vehicle CategoryTypical Flywheel HPAverage Weight0-60 mph Time
Economy Hatchback / Sedan120 - 180 HP2,800 lbs8.5 - 10.0 s
Midsize Crossover / SUV200 - 290 HP4,000 lbs7.0 - 8.5 s
Hot Hatch / Sport Sedan300 - 400 HP3,400 lbs4.5 - 5.5 s
V8 Muscle Car / Track Car450 - 650 HP3,800 lbs3.5 - 4.2 s
Supercar (Exotic)650 - 800 HP3,300 lbs2.8 - 3.2 s
Electric Hypercar1,000 - 2,000 HP4,500 lbs1.8 - 2.4 s

Frequently Asked Questions

What is horsepower and what is the exact formula from torque and RPM?
Horsepower (HP) is the engineering rate of mechanical work delivery. The standard SAE formula is: HP = (Torque in lb-ft × RPM) ÷ 5,252. The 5,252 divisor originates mathematically from James Watt's definition of 1 HP (33,000 ft-lb/min) divided by 2π radians per revolution.
What is the difference between BHP, WHP, and Metric PS?
BHP (Brake Horsepower) measures net power output at the engine flywheel before mechanical transmission drag. WHP (Wheel Horsepower) measures the actual power transferred to the asphalt on a chassis dynamometer after transmission, driveshaft, and differential parasitic losses (10-25%). Metric HP (PS / CV) equals 0.9863 standard imperial horsepower.
Why do torque and horsepower curves always cross at 5,252 RPM?
Because HP = (Torque × RPM) / 5,252, when RPM is exactly 5,252, the equation simplifies to HP = Torque × (5,252 / 5,252) = Torque. Thus, whenever dyno graphs plot torque in lb-ft and power in HP on identical vertical scales, the curves mathematically intersect at 5,252 RPM.
How do you estimate horsepower from quarter-mile ET and vehicle weight?
Using the established Hale/Fox drag racing kinematic empirical formula: HP = Weight (lbs) ÷ (ET ÷ 5.825)³. For instance, a 3,500 lb vehicle finishing the quarter-mile in 12.0 seconds produces approximately: 3,500 ÷ (12.0 ÷ 5.825)³ ≈ 400 flywheel HP.

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