kW to Nm Calculator
Power on its own does not tell you torque. Enter the kilowatts and the RPM they are produced at, and this returns the torque in newton metres.
Torque and power are not two names for the same thing, and you cannot convert one into the other without knowing the speed the engine or motor is turning at. That single requirement is what most kW to Nm tools skip over — and it is the reason two engines with identical kW figures can feel completely different to drive.
Why You Cannot Convert kW to Nm Without RPM
Power is the rate at which work is done. Torque is a twisting force. The link between them is rotational speed: the same power produces a lot of torque at low RPM and much less at high RPM, because the force is being delivered over more revolutions per second.
This is why the question "how many Nm is 125 kW?" has no single answer. At 2,000 RPM it is 597 Nm. At 6,000 RPM the same 125 kW is only 199 Nm — a third as much. Any tool that returns a torque figure without asking for RPM is either assuming a value silently or is simply wrong.
| Power | At 2,000 RPM | At 4,000 RPM | At 6,000 RPM | At 8,000 RPM |
|---|---|---|---|---|
| 75 kW | 358 Nm | 179 Nm | 119 Nm | 90 Nm |
| 100 kW | 477 Nm | 239 Nm | 159 Nm | 119 Nm |
| 125 kW | 597 Nm | 298 Nm | 199 Nm | 149 Nm |
| 150 kW | 716 Nm | 358 Nm | 239 Nm | 179 Nm |
| 200 kW | 955 Nm | 477 Nm | 318 Nm | 239 Nm |
Where the 9549 Constant Comes From
It is not an arbitrary number. Power in watts equals torque in newton metres multiplied by angular velocity in radians per second. Converting RPM into radians per second means multiplying by 2π and dividing by 60, and converting watts into kilowatts means dividing by 1,000. Fold those together and you get:
Using This for Electric Motors
Motor nameplates give rated power in kW and rated speed in RPM, so the full-load torque follows directly. A 7.5 kW motor rated at 1,450 RPM produces about 49 Nm at full load.
Two cautions apply. First, the nameplate speed is the loaded speed, not the synchronous speed — using 1,500 RPM instead of 1,450 for a four-pole motor understates torque by about 3%. Second, induction motors produce considerably more than rated torque at start-up, typically 150–250% of full load, which is what matters when sizing for a hard-starting load.
Peak Power and Peak Torque Happen at Different Speeds
Because torque falls as RPM rises for a given power, an engine's peak torque almost always occurs well below its peak power. A modern turbocharged car might make maximum torque from 1,800 RPM while peak power arrives near 5,500 RPM. Feeding peak power and peak-torque RPM into this calculator together will not reproduce the quoted torque figure, because those two numbers come from different points on the curve.
To convert in the other direction, use our Nm to kW calculator. For imperial units, HP to torque works in pound-feet, and Nm to lb-ft converts between the two torque units. The underlying relationship is explained in horsepower vs torque.
Frequently Asked Questions
Multiply kilowatts by 9549 and divide by RPM. For example, 125 kW at 4,000 RPM = 125 × 9549 ÷ 4000 = 298 Nm.
No. Power and torque are different quantities linked by rotational speed. The same power gives high torque at low RPM and low torque at high RPM, so a torque figure is meaningless without the speed it applies to.
It converts between units. Power in watts equals torque × angular velocity in rad/s. Converting RPM to rad/s and watts to kW folds into 60 × 1000 ÷ 2π = 9549.3.
It depends on RPM. At 2,000 RPM it is 477 Nm; at 4,000 RPM, 239 Nm; at 6,000 RPM, 159 Nm. There is no single answer without a stated speed.
The exact value is 9549.30. Both 9549 and 9550 appear in references; the difference is about 0.007% — far below any dyno's measurement error.
Use nameplate rated power and rated speed. A 7.5 kW motor at 1,450 RPM gives 7.5 × 9549 ÷ 1450 ≈ 49 Nm at full load. Use the loaded speed, not synchronous speed.
Because peak power and peak torque occur at different engine speeds. Manufacturers quote max power at one RPM and max torque at a lower one, so combining the two headline numbers will not reproduce either.