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About This Calculator
Horsepower is a unit of power originally defined by James Watt to compare steam engine output to draft horses. This calculator converts between mechanical, electrical, and metric horsepower while also computing power from torque and RPM. It's essential for evaluating engine performance, motor specifications, and machinery capacity.
Quick Tips
- 1 One mechanical horsepower equals exactly 745.7 watts of electrical power.
- 2 Torque times RPM divided by 5252 gives horsepower for rotating engines.
- 3 Brake horsepower measures output at the flywheel, not at the wheels.
Example Calculation
Engine produces 350 lb-ft of torque at 4,500 RPM.
Horsepower: 300 HP (223.7 kW) | Formula: (350 x 4500) / 5252 = 300 HP
The Horsepower Formula
Horsepower is calculated as HP = (Torque x RPM) / 5,252. The constant 5,252 comes from the relationship between rotational and linear work. At exactly 5,252 RPM, horsepower and torque are always equal.
Torque vs Horsepower
Torque is the twisting force the engine produces, measured in pound-feet. Horsepower is the rate at which work is done, combining torque and speed. Torque determines acceleration from a stop, while horsepower determines top speed and sustained performance.
HP, kW, and Metric HP
One mechanical horsepower equals 0.7457 kilowatts (kW). One metric horsepower (PS) equals 0.9863 mechanical HP. European cars often list power in kW or PS. This calculator converts between all three units.
Horsepower at the Wheels vs Engine
Brake horsepower (BHP) is measured at the engine output. Wheel horsepower (WHP) is measured at the wheels after drivetrain losses. Automatic transmissions lose about 15-20% and manual transmissions lose about 10-15% of engine power.
Frequently Asked Questions
BHP (brake horsepower) is the power measured at the engine crankshaft. HP (horsepower) is a general term. WHP (wheel horsepower) is measured at the wheels. Due to drivetrain losses, WHP is always lower than BHP.
At exactly 5,252 RPM, horsepower and torque values are always equal. Below this RPM, torque is higher than horsepower. Above it, horsepower exceeds torque. This is a mathematical fact of the HP = (T x RPM) / 5,252 formula.
Multiply horsepower by 0.7457 to get kilowatts. For example, 300 HP equals about 224 kW. Conversely, multiply kW by 1.341 to convert to HP. Electric vehicle specifications typically use kW.
Economy cars have 100-150 HP, mid-size sedans 180-250 HP, performance sedans 300-400 HP, and sports cars 400+ HP. Horsepower needs depend on vehicle weight, intended use, and personal preference.