Torque to Horsepower Calculator
Convert torque (lb-ft) and RPM to horsepower instantly using HP = Torque x RPM / 5252. Free engine power calculator with kW conversion for automotive use.
About This Calculator
The Torque to Horsepower Calculator uses the classic engine formula HP = Torque (lb-ft) x RPM / 5252 to convert rotational force and speed into power output. Whether you are tuning a race car, sizing an industrial motor, or comparing marine engines, this tool provides instant horsepower and kilowatt results.
The constant 5252 is derived from James Watt's definition of horsepower (33,000 ft-lb/min) divided by 2pi (the distance traveled per revolution in radians). At 5,252 RPM, torque and horsepower values are numerically equal. The calculator also displays the equivalent power in kilowatts (kW), the standard SI unit used internationally.
Formula
Horsepower (HP) = Torque (lb-ft) x RPM ÷ 5252
Kilowatts (kW) = HP x 0.7457
Regional Notes
- United States: Horsepower (HP) is the primary unit for engine power in automotive, marine, and industrial applications. Torque is typically measured in lb-ft.
- United Kingdom: While horsepower is still commonly used for vehicle advertising, kilowatts (kW) are increasingly adopted for official vehicle specifications and industrial motor ratings per EU/UK regulations.
- India: Both horsepower and kilowatts are used across applications. Automotive manufacturers typically advertise power in HP (or PS), while industrial motors and generators are rated in kW.
Typical Power Ranges
- Compact cars: 100-200 HP (74-149 kW)
- Sports cars: 300-700 HP (224-522 kW)
- Trucks and SUVs: 250-450 HP (186-336 kW)
- Motorcycles: 50-200 HP (37-149 kW)
- Small marine outboards: 10-300 HP (7.5-224 kW)
Frequently Asked Questions
How is horsepower calculated from torque?
Horsepower is calculated using the formula HP = Torque (lb-ft) x RPM / 5252. This formula was derived by James Watt and represents the rate at which work is done. The constant 5252 comes from the conversion factors: 1 HP = 33,000 ft-lb/min, and the circumference of a 1-foot radius circle is 2pi feet.
Why is 5252 used in the horsepower formula?
The number 5252 is the constant where torque and horsepower curves cross. It comes from 33,000 (ft-lb per minute per HP) divided by 2pi (the circumference of a 1-foot radius circle in radians): 33,000 / (2 x pi) = 5,252. This means at 5,252 RPM, torque and horsepower values are equal.
What is the difference between torque and horsepower?
Torque measures rotational force (pulling power), while horsepower measures the rate at which work is done (power output). A diesel engine may have high torque at low RPM for towing, while a sports car engine produces peak horsepower at high RPM for speed. Both are essential for understanding engine performance.
How do I convert horsepower to kilowatts?
To convert horsepower to kilowatts, multiply by 0.7457: kW = HP x 0.7457. Conversely, to convert kW to HP, divide by 0.7457. The UK and Europe typically use kW for engine power ratings, while the US uses HP. Australia and many Asian countries use both units depending on the application.
What are typical torque and horsepower values?
Compact cars produce 100-200 HP with 100-200 lb-ft torque. Sports cars produce 300-700 HP with 250-650 lb-ft. Trucks and SUVs produce 250-450 HP with 300-800 lb-ft torque. High-performance electric vehicles can produce 500-1000+ HP with instant torque from 0 RPM.
What is the relationship between RPM and power?
Power (horsepower) increases linearly with RPM for a given torque. An engine producing 300 lb-ft of torque at 3,000 RPM makes 171 HP (300 x 3000 / 5252), while the same torque at 6,000 RPM makes 342 HP. This is why high-revving engines can produce more power despite similar torque figures.
How is kilowatt (kW) related to horsepower?
One horsepower equals 0.7457 kilowatts. Conversely, one kilowatt equals 1.341 horsepower. The kW is the SI unit of power used internationally. Most countries outside the US use kW for engine power ratings. For reference, a 100 HP engine produces approximately 74.57 kW.