Horsepower Calculator
Calculate engine power output from RPM and torque
Horsepower (HP) is a unit of power that measures the rate at which work is done. Originally defined by James Watt, one horsepower equals approximately 746 watts or 0.746 kilowatts.
In automotive applications, horsepower is used to:
- Measure engine output power
- Compare vehicle performance
- Determine power-to-weight ratios
- Calculate acceleration potential
Understanding horsepower is crucial for engine tuning, performance modifications, and vehicle selection.
Horsepower can be calculated using the following formula:
HP = (Torque × RPM) ÷ 5252
Where:
- Torque is in pound-feet (lb-ft)
- RPM is engine speed in revolutions per minute
- 5252 is a constant derived from the definition of horsepower
This formula is based on the relationship between torque, RPM, and power in a rotating system.
Power and torque are related but distinct measurements:
- Torque: The rotational force produced by the engine, measured in pound-feet (lb-ft) or Newton-meters (Nm).
- Power: The rate at which work is done, calculated from torque and engine speed.
Key differences:
- Torque determines acceleration and pulling power
- Horsepower determines top speed and sustained performance
- Peak torque and peak horsepower typically occur at different RPMs
Common power unit conversions:
- 1 Horsepower (HP) = 746 Watts (W)
- 1 Horsepower (HP) = 0.746 Kilowatts (kW)
- 1 Kilowatt (kW) = 1.341 Horsepower (HP)
- 1 Metric Horsepower (PS) = 0.986 HP
Torque conversions:
- 1 pound-foot (lb-ft) = 1.356 Newton-meters (Nm)
- 1 Newton-meter (Nm) = 0.738 pound-feet (lb-ft)
Why does horsepower peak at higher RPMs than torque?
Horsepower increases with RPM because it's a function of both torque and engine speed. Even as torque begins to drop at higher RPMs, the increasing engine speed can result in higher horsepower.
What's more important: horsepower or torque?
Both are important for different aspects of vehicle performance. Torque is crucial for initial acceleration and pulling power, while horsepower determines top speed and high-end performance. The ideal balance depends on the vehicle's intended use.
Why is the number 5252 used in the horsepower formula?
5252 is derived from the mathematical relationship between horsepower, torque, and RPM. It comes from converting the original definition of horsepower (33,000 ft-lbs per minute) into a more usable form for rotating machinery.