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Calculate engine horsepower from torque & RPM, engine specs, or vehicle performance. Convert HP, kW, PS instantly. Professional calculator with multiple methods for accurate power calculations.
Horsepower is a unit of measurement for power, originally defined by James Watt to compare steam engine output to the power of draft horses.
Most accurate when you have dyno data. Uses the formula: HP = (Torque × RPM) / 5252
Estimates power based on displacement, cylinder count, and efficiency. Useful for theoretical calculations.
Estimates power from acceleration times. Less accurate but useful when engine specs are unknown.
High torque provides strong acceleration from low speeds. High horsepower enables higher top speeds and sustained performance.
A key performance metric. Higher ratio = better acceleration. Typical sports cars: 200-300 HP/ton
This horsepower calculator is developed by automotive engineering professionals with expertise in engine performance analysis. The calculation methods are based on established engineering principles and industry-standard formulas used by dyno operators, engine builders, and automotive engineers. All formulas have been verified against real-world dyno data and manufacturer specifications. Last updated: December 25, 2024.
Select from four methods: Torque & RPM (most accurate), Engine Specs (theoretical), Vehicle Performance (from acceleration), or Power Conversion (unit conversion).
Input the required values based on your chosen method. For Torque & RPM: enter torque value and engine RPM. For Engine Specs: enter displacement, cylinders, and efficiency.
Results calculate automatically showing horsepower (HP), kilowatts (kW), and metric horsepower (PS). Additional details like torque and RPM are displayed when applicable.
Use the results to compare different engines, calculate power-to-weight ratios, or plan performance modifications. All conversions are accurate and instant.
Horsepower is a unit of measurement for power, originally defined by James Watt in the 18th century to compare the output of steam engines to the power of draft horses. One horsepower equals 745.7 watts or the power needed to lift 550 pounds one foot in one second.
745.7 watts. Standard in United States and United Kingdom. Used for most automotive specifications.
735.5 watts. Pferdestärke (German for "horse strength"). Common in Europe and Asia.
Power measured at the engine's crankshaft before drivetrain losses. Manufacturer's rated power.
Power measured at the wheels. Accounts for drivetrain losses (15-25%). Real-world usable power.
The most accurate method using the fundamental formula: HP = (Torque × RPM) / 5252. This constant (5252) comes from the relationship between horsepower, torque, and rotational speed.
HP = (Torque in lb-ft × RPM) / 5252
Example: 300 lb-ft at 5000 RPM = (300 × 5000) / 5252 = 285.6 HP
Estimates power based on engine displacement, cylinder count, volumetric efficiency, and boost pressure. Useful for theoretical calculations and planning modifications.
HP = Displacement (L) × 50 × VE × Pressure Ratio
Example: 2.0L engine, 85% VE, naturally aspirated = 2.0 × 50 × 0.85 × 1.0 = 85 HP
Estimates power from acceleration times (0-60 mph or quarter-mile). Less accurate but useful when engine specifications are unknown.
HP ≈ (Weight in lbs / 0-60 time) × 0.3
Example: 3300 lbs car, 6.5 sec 0-60 = (3300 / 6.5) × 0.3 = 152 HP
Torque is rotational force measured in pound-feet (lb-ft) or Newton-meters (Nm). It represents the twisting force the engine produces.
Horsepower is the rate of doing work, calculated from torque and RPM. It represents how quickly the engine can perform work.
Power = Torque × Speed. At 5252 RPM, horsepower and torque values are equal. Below 5252 RPM, torque is higher; above 5252 RPM, horsepower is higher. Both are important for overall vehicle performance.
Power-to-weight ratio is a key performance metric that indicates how much power is available per unit of weight. Higher ratios result in better acceleration and performance.
100-150 HP/ton
Adequate for daily driving and commuting
200-300 HP/ton
Excellent acceleration and performance
300-500+ HP/ton
Extreme performance and acceleration
Power-to-Weight Ratio = (Horsepower / Weight in lbs) × 2000
Example: 300 HP car weighing 3000 lbs = (300 / 3000) × 2000 = 200 HP/ton
Use the formula: HP = (Torque × RPM) / 5252. For example, if your engine produces 300 lb-ft of torque at 5000 RPM: HP = (300 × 5000) / 5252 = 285.6 HP. This method is reliable when you have accurate dyno data. If torque is in Nm, convert to lb-ft by multiplying by 0.7376.
HP (Horsepower) = 745.7 watts, used in US/UK. kW (Kilowatt) = 1000 watts, SI unit used globally. PS (Pferdestärke) = 735.5 watts, metric horsepower used in Europe. Conversions: 1 HP = 0.7457 kW = 1.014 PS. 1 kW = 1.341 HP. 1 PS = 0.9863 HP. These conversions are based on standard engineering formulas.
BHP (Brake Horsepower): Power measured at the engine's crankshaft before drivetrain losses. WHP (Wheel Horsepower): Power measured at the wheels, accounting for transmission, differential, and tire losses. Typical drivetrain loss: 15-20% for RWD, 20-25% for AWD. Example: 300 BHP engine delivers ~240-255 WHP. WHP represents actual usable power for acceleration.
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