Torque & Power Conversion Calculator (HP to kW)

Converting rotational torque and RPM into power output

50 Nm of torque at 3,000 RPM converts to 15.71 kilowatts, equivalently 21.07 horsepower -- power output from a rotating shaft depends on both how much twisting force is applied (torque) and how fast it's spinning (RPM), not on either one alone.

The formula kW = torque(Nm) x RPM / 9549 packs a specific unit-conversion constant (9549) into a single number, derived from converting RPM into radians per second and combining that with the basic power = torque x angular velocity relationship -- the constant exists purely to let you skip several intermediate conversion steps.

The same torque at a different RPM produces proportionally different power -- doubling RPM to 6,000 while keeping torque at 50 Nm would double power output to roughly 31.4 kW, since power scales linearly with rotational speed for a fixed torque.

Why horsepower and kilowatts use different conversion factors

kW = torque(Nm) x rpm / 9549. Mechanical HP uses 0.7457 kW. Converting from kilowatts to (mechanical) horsepower uses a fixed ratio: 1 horsepower = 0.7457 kW, so 15.71 kW / 0.7457 = 21.07 hp -- this specific 'mechanical horsepower' definition is the most common one used in engine and motor specifications, though a couple of other historical horsepower definitions exist with slightly different conversion factors.

This calculator can also solve in the reverse direction -- starting from a known horsepower figure and RPM to find the resulting torque, using the same underlying relationship rearranged, which is useful when a spec sheet gives horsepower but you need to know the actual torque at a specific RPM.

Real engines and motors don't produce constant torque across their entire RPM range -- a single torque-and-RPM pair like this example represents one specific operating point, not the full torque curve a real motor would show across its usable speed range.

Related mechanical and unit-conversion tools

For converting the resulting power figure into other energy or power-related units, the Energy Unit Converter covers related unit conversions.

For the force-and-motion relationship that produces torque in the first place, the Force, Mass & Acceleration Calculator is a related foundational physics tool.

Frequently Asked Questions (FAQ)