Electric Motor Torque Calculator for kW, HP and RPM

Electric motor sizing always comes back to the relationship between power, torque, and rotational speed. This calculator uses the two common engineering shortcuts for that relationship. In metric form, torque in newton-meters is T = (P × 9549.3) / n when power is entered in kilowatts and speed is in revolutions per minute. In imperial form, torque in pound-feet is T = (HP × 5252) / RPM when power is in horsepower. These constants simply package the unit conversions that come from the more fundamental power equation P = Tω. When you know power and speed, torque tells you how much twisting force the motor can deliver at the shaft. That number matters for conveyors, pumps, compressors, gearboxes, hoists, machine tools, and any other rotating load that must overcome inertia or resistive force. A motor with high speed but low torque may not start a heavy load reliably, while a lower-speed motor with more torque may perform much better in the same application. The calculator helps you see that tradeoff immediately. The reverse calculations are just as useful. If you already know the required torque and intended operating speed, solving for power lets you estimate the motor size needed for the job. If you know the available power and required torque, solving for speed reveals the shaft RPM you can expect before gearing. These quick relationships are widely used during concept design, troubleshooting, and specification review because they provide a fast first-pass answer without requiring a full motor model. Unit handling is often where mistakes happen. Many catalogs list motor output in kilowatts, but older equipment data sheets may use horsepower. Torque can likewise appear in Nm or ft·lb depending on industry and region. This calculator keeps the selected power unit tied to the proper constant and also shows converted values, so you can compare a metric motor spec against an imperial service manual without reworking the math by hand. Remember that these formulas describe mechanical output at the shaft, not electrical input at the terminals. Real motor selection must still account for efficiency, service factor, starting current, gearbox losses, duty cycle, temperature rise, and transient load conditions. Even with those caveats, the speed-power-torque triangle remains one of the most practical checks a designer or technician can make, and it is exactly what this calculator is built to streamline.