Torque to HP Calculator
Enter torque and RPM to calculate horsepower and kilowatts, or enter HP and RPM to back-calculate torque. Choose pound-feet or Newton-meters, add an optional vehicle weight for power-to-weight ratio, and see the full worked calculation. The result updates as you type.
Formula
Worked example
A V8 engine produces 350 lb-ft of torque at 5,000 RPM. HP = 350 x 5,000 / 5,252 = 333.2 HP (248.5 kW). At 5,252 RPM, HP would equal 350, the same as the torque value. If the vehicle weighs 3,500 lbs, its power-to-weight ratio is (333.2 / 3,500) x 1,000 = 95.2 HP per 1,000 lbs.
The torque to horsepower formula
Horsepower and torque are two ways of describing the same underlying power, related by rotational speed. The formula is: HP = Torque (lb-ft) x RPM / 5,252. The constant 5,252 comes from unit conversion: one mechanical horsepower equals 33,000 foot-pounds per minute, and dividing that by 2 x pi (to convert revolutions to radians) gives 5,252.11. In SI units, Power (kW) = Torque (N-m) x RPM / 9,549.3. This calculator works both directions: give it torque and RPM to get HP, or give it HP and RPM to find the torque needed.
Why HP and torque curves always cross at 5,252 RPM
When an engine's torque is plotted in lb-ft and horsepower on the same axis, the two curves always intersect at exactly 5,252 RPM. At that point, the numerical values are identical. Below 5,252 RPM, torque (lb-ft) is the larger number. Above 5,252 RPM, horsepower is the larger number. This is a direct consequence of the formula HP = Torque x RPM / 5,252: when RPM equals 5,252, HP equals Torque exactly. Understanding this crossover helps you read a dyno chart correctly and explains why high-revving engines produce high HP figures even with relatively modest torque.
Torque vs. horsepower in everyday driving
Torque describes how hard an engine can twist, which translates to acceleration from a stop, towing capacity, and climbing hills. Horsepower describes how fast an engine can do work, which relates to top speed and sustained high-speed performance. A diesel truck may produce 500 lb-ft of torque at just 1,800 RPM, giving enormous pulling force. A naturally aspirated sports car may produce only 300 lb-ft but rev to 8,000 RPM, reaching over 450 HP. Both engines can produce similar peak HP through very different torque and RPM profiles. For towing, high low-RPM torque wins. For track use, high peak HP often matters more.
Power-to-weight ratio and vehicle performance
Absolute horsepower tells you how much power is available. Power-to-weight ratio tells you how well that power can accelerate the vehicle. The standard US measure is HP per 1,000 lbs. Economy cars typically achieve 50-70 HP per 1,000 lbs. Performance sports cars reach 100-150. Supercars like the Porsche 911 Turbo S deliver around 200 HP per 1,000 lbs. Formula 1 cars exceed 1,000 HP per 1,000 lbs. Enter your vehicle weight in this calculator to see where your engine falls. Metric users can use HP per tonne (1,000 kg), which gives numerically similar results to HP per 1,000 lbs since 1,000 lbs is about 454 kg.
HP and torque at common RPM values (for your torque setting)
| RPM | HP | kW | Note |
|---|---|---|---|
| 1000 | varies | varies | Low idle range |
| 2000 | varies | varies | City driving range |
| 3000 | varies | varies | Highway cruise range |
| 5252 | varies | varies | HP = Torque (lb-ft) always |
| 6000 | varies | varies | High performance range |
| 8000 | varies | varies | Racing / redline range |
Shows how HP changes with RPM when torque is held constant at the value you entered. HP = Torque x RPM / 5,252.
Frequently asked questions
What is the formula to convert torque to horsepower?
HP = Torque (lb-ft) x RPM / 5,252. In metric units: Power (kW) = Torque (N-m) x RPM / 9,549.3. You always need both torque and rotational speed (RPM) to calculate power because power is the rate at which work is done, and a torque value alone does not tell you how fast the shaft is turning.
Why do I need RPM to convert torque to HP?
Because power depends on both how hard the engine is pushing (torque) and how fast it is spinning (RPM). Imagine tightening a bolt: you can apply 100 lb-ft of force to a wrench, but if nothing is moving, no power is being transferred. Power only appears when the shaft actually rotates. A 400 lb-ft engine at 4,000 RPM produces 304 HP. That same 400 lb-ft at 2,000 RPM produces only 152 HP.
Where does the 5,252 constant come from?
One mechanical horsepower equals exactly 33,000 foot-pounds per minute. To convert from torque (which is in foot-pounds, a static measure) to power per revolution, you multiply torque by RPM and then divide by 33,000 / (2 x pi) = 5,252.11. The 2 x pi converts one full revolution into the angle in radians, which is needed to go from force at a distance (lb-ft) to actual work. So 5,252 is not an arbitrary constant but a precise consequence of the definition of horsepower.
How do I convert Newton-meters to pound-feet?
1 lb-ft = 1.35582 N-m, so 1 N-m = 0.73756 lb-ft. To convert N-m to lb-ft, divide by 1.3558 (or multiply by 0.7376). For example, 400 N-m = 400 / 1.3558 = 295.0 lb-ft. This calculator handles the conversion automatically when you select the N-m input option.
What is a good power-to-weight ratio for a car?
For US measurements (HP per 1,000 lbs): under 50 is typical for economy and large SUVs; 50-100 is the range for normal sports cars and performance sedans; 100-200 is high performance territory covering supercars and muscle cars; above 200 is exotic or purpose-built race car territory. The legendary Dodge Viper SRT-10 produced about 150 HP/1,000 lbs. A Bugatti Chiron exceeds 400 HP/1,000 lbs.
Can I use this to calculate electric motor power?
Yes. Electric motors also obey the same physics: Power (kW) = Torque (N-m) x RPM / 9,549.3. Select N-m as your torque unit and enter the motor's rated torque and RPM. Keep in mind that electric motors often produce peak torque from 0 RPM and have different torque-RPM profiles from combustion engines, so their peak HP figure appears at a higher RPM than where peak torque is.
What is the difference between mechanical, metric, and electrical horsepower?
Mechanical HP (used in the US) = 550 ft-lbf/s = 745.7 W. Metric HP (used in Europe) = 75 kgf-m/s = 735.5 W. Electrical HP = exactly 746 W. The differences are small (under 1.5%), so for most practical purposes they are interchangeable. This calculator uses mechanical HP, which is standard for automotive performance ratings in North America.