6.71
hp
5,000
W
5
kW
17,060.7
BTU/hr
6.8
PS
6.71
hp
5,000
W
5
kW
17,060.7
BTU/hr
6.8
PS
Horsepower (hp) is a unit of power introduced by James Watt in the 18th century to compare steam engine output to the work of draft horses. Despite the rise of SI units, horsepower remains widely used in automotive, marine, and aviation industries to rate engine performance. One mechanical horsepower equals approximately 745.7 watts or 550 foot-pounds per second.
This Horsepower Calculator operates in three modes: convert watts to horsepower, calculate horsepower from torque and RPM, or convert horsepower back to watts. The torque-RPM formula $$HP = \frac{T \times RPM}{5252}$$ is especially important in automotive engineering, where dynamometer testing measures engine torque at various speeds to determine the power curve. Results are also provided in kilowatts and BTU/hr for HVAC and international applications. Whether you are evaluating a car engine, sizing an electric motor, or comparing equipment specifications, this calculator bridges the gap between power unit systems.
Three conversion paths are available:
Watts to HP: $$HP = \frac{W}{745.7}$$
Torque + RPM to HP: $$HP = \frac{T \times RPM}{5252}$$
where $$T$$ is torque in pound-feet (lb·ft) and the constant 5252 comes from $$\frac{33000}{2\pi}$$ (since 1 hp = 33,000 ft·lb/min).
HP to Watts: $$W = HP \times 745.7$$
BTU/hr conversion: $$1 \text{ hp} = 2544.43 \text{ BTU/hr}$$. Note that there are several definitions of horsepower — this calculator uses mechanical (imperial) horsepower, the most common in the US and UK automotive industries.
A typical car engine produces 100–400 hp. A riding lawn mower is about 15–25 hp. A human can sustain about 0.1 hp (75 W) continuously, or briefly achieve 1–2 hp during peak exertion. In electric vehicles, motors are often rated in kW: a 150 kW motor equals about 201 hp. The torque-RPM relationship shows that peak horsepower occurs where the torque × RPM product is maximized.
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A 7500 W (7.5 kW) electric motor is rated at approximately 10.06 hp.
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An engine producing 280 lb·ft at 5500 RPM delivers HP = 280 × 5500 / 5252 ≈ 293 hp (218.6 kW).
The constant 5252 equals 33,000 / (2π), derived from the definition that 1 hp = 33,000 ft·lb/min. Since rotational power is $$P = 2\pi \times T \times RPM$$, dividing by 33,000 ft·lb/min/hp gives the factor 5252. At exactly 5252 RPM, horsepower numerically equals torque.
BHP (brake horsepower) is measured at the engine crankshaft using a dynamometer (brake). HP at the wheels (WHP) is lower due to drivetrain losses (transmission, differential). Typically WHP ≈ 80–90% of BHP.
Common types: Mechanical/Imperial HP = 745.7 W (used here), Metric HP (PS) = 735.5 W, Electrical HP = 746 W, Boiler HP = 9,809.5 W. Always check which definition is being used when comparing specifications.
1 metric HP (PS, Pferdestärke) = 0.9863 mechanical HP. So 100 PS ≈ 98.63 hp. The difference is small (about 1.4%) but matters for precise engineering specifications. European cars often use PS/kW.
Torque is rotational force (how hard the engine twists). Horsepower is torque multiplied by rotational speed (how fast the engine delivers that twist). Torque determines pulling/acceleration ability; horsepower determines top speed and sustained performance.
Ironically, a horse can produce about 14.9 hp in short bursts. The 1 hp definition was based on sustained work output — specifically, a horse turning a mill wheel continuously. Modern measurements show average sustained horse power is closer to 0.7 hp.
Roboculator Team
The Roboculator Team explains calculations, planning tools, and practical formulas in clear language for real-life situations.
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