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Convert between horsepower, kilowatts, watts, and BTU/hr. Calculate engine horsepower, motor power requirements, and compare mechanical and electrical power ratings.
Everything you need to know
Horsepower (hp) is one of the most recognized units of power, especially in automotive and mechanical engineering. Originally defined by James Watt in the 18th century to compare steam engines to draft horses, it remains the standard for rating engines, motors, and machinery today.
Our calculator converts between all common power units and helps you understand the relationship between mechanical horsepower, metric horsepower, kilowatts, and other power measurements.
James Watt determined that a draft horse could turn a mill wheel 144 times per hour, creating a power output he defined as one horsepower. Modern definitions vary slightly:
| Unit | Definition | Equivalent |
|---|---|---|
| Mechanical HP (hp) | 550 ft-lb/s | 745.7 watts |
| Metric HP (PS) | 75 kg-m/s | 735.5 watts |
| Electrical HP | 746 watts | Exactly 746 W |
| Boiler HP | 34.5 lb steam/hr | 9,809.5 watts |
kW = hp × 0.7457
Example: 300 hp car engine kW = 300 × 0.7457 = 223.7 kW
hp = kW ÷ 0.7457
Example: 150 kW electric motor hp = 150 ÷ 0.7457 = 201.1 hp
hp = W ÷ 745.7
hp = BTU/hr ÷ 2,545
| Vehicle | Horsepower | Kilowatts | Notes |
|---|---|---|---|
| Compact car (Toyota Corolla) | 169 hp | 126 kW | 2.0L engine |
| Midsize sedan (Honda Accord) | 192 hp | 143 kW | Turbo 1.5L |
| Sports car (Ford Mustang GT) | 450 hp | 336 kW | 5.0L V8 |
| Supercar (Ferrari F8) | 710 hp | 529 kW | Twin-turbo V8 |
| Hypercar (Bugatti Chiron) | 1,479 hp | 1,103 kW | Quad-turbo W16 |
| Tesla Model 3 (Performance) | 450 hp | 335 kW | Dual motors |
| Ford F-150 (V6) | 400 hp | 298 kW | 3.5L EcoBoost |
| Motorcycle (Harley-Davidson) | 90 hp | 67 kW | Cruiser |
| Motorcycle (Kawasaki Ninja) | 200 hp | 149 kW | Sportbike |
| Device | Horsepower | Watts | Notes |
|---|---|---|---|
| Ceiling fan | 0.05-0.1 hp | 37-75 W | |
| Refrigerator compressor | 0.25-0.5 hp | 186-373 W | |
| Washing machine motor | 0.5-1 hp | 373-746 W | |
| Garage door opener | 0.5-1 hp | 373-746 W | |
| Table saw | 1.5-3 hp | 1,120-2,240 W | |
| Air conditioner (3-ton) | 4.5 hp | 3,500 W | |
| Pool pump | 1-3 hp | 746-2,240 W | |
| Elevator motor | 10-50 hp | 7,457-37,285 W | |
| Industrial compressor | 50-500 hp | 37-373 kW |
HP = (Torque × RPM) ÷ 5,252
Where torque is in pound-feet (lb-ft).
Example: Engine produces 300 lb-ft at 4,000 RPM HP = (300 × 4,000) ÷ 5,252 = 228.5 hp
HP = (Weight × Velocity²) ÷ (Elapsed Time × 550 × Factor)
Approximate method for quarter-mile times: HP ≈ Weight ÷ (ET ÷ 5.825)³
Example: 3,500 lb car runs quarter-mile in 13.5 seconds HP ≈ 3,500 ÷ (13.5 ÷ 5.825)³ = 3,500 ÷ 12.4 = 282 hp
HP ≈ (Top Speed in MPH ÷ 3)³ × (Drag Coefficient × Frontal Area)
| Horsepower | Torque | |
|---|---|---|
| What it measures | Rate of work | Twisting force |
| Feels like | Top speed, acceleration at high RPM | Initial "push" off the line |
| Important for | Racing, highway passing | Towing, off-roading, daily driving |
| Analogy | How fast you can run | How much you can lift |
Key insight: Horsepower = Torque × RPM. You can have high torque at low RPM (trucks) or lower torque at high RPM (sports cars). Both can produce the same horsepower.
Power-to-weight is often more important than raw horsepower:
| Vehicle | Weight | HP | HP/Ton | 0-60 mph |
|---|---|---|---|---|
| Ford Fiesta ST | 2,700 lb | 197 hp | 146 | 6.5 sec |
| Ford Mustang GT | 3,700 lb | 450 hp | 243 | 4.0 sec |
| Porsche 911 GT3 | 3,100 lb | 502 hp | 324 | 3.0 sec |
| Ferrari SF90 | 3,500 lb | 986 hp | 564 | 2.5 sec |
| Bugatti Chiron | 4,400 lb | 1,479 hp | 672 | 2.4 sec |
| Tesla Model S Plaid | 4,800 lb | 1,020 hp | 425 | 1.99 sec |
| F1 Car (2023) | 1,760 lb | 1,000+ hp | 1,136 | ~2.0 sec |
Most countries use the metric system. PS (Pferdestärke, or metric horsepower) is common in Germany. kW is the SI standard unit. 1 PS = 0.986 hp.
A real horse can sustain about 0.7-0.9 hp over a workday. Watt's definition was based on peak output over short periods.
Technically yes (both measure power), but electric motors deliver instant torque and maintain power across a wider RPM range. A 300 hp electric car often feels faster than a 300 hp gas car.
Determine the load (weight, speed, incline), calculate the work required, add a safety factor (usually 1.5×), and select a motor accordingly.
Brake horsepower (bhp) is measured at the engine's crankshaft before drivetrain losses. Wheel horsepower (whp) is measured at the wheels and is typically 15-20% lower due to transmission and drivetrain friction.