Motor Output Torque Calculator

Calculator Input

Calculation source

Known power

Known power unit

Known power basis

Electrical supply type

Voltage

Current

Power factor

Motor efficiency (%)

Motor speed (rpm)

Reduction ratio

Drivetrain efficiency (%)

Service factor

Formula Used

Torque: T = P × 60 ÷ (2 × π × N)

Metric shortcut: T = 9550 × P(kW) ÷ N(rpm)

Output speed: Output rpm = Motor rpm ÷ Reduction ratio

Output shaft power: Shaft power = Motor output power × Drivetrain efficiency

Design torque: Design torque = Output shaft torque × Service factor

Single phase input power: P = V × I × PF

Three phase input power: P = √3 × V × I × PF

DC input power: P = V × I

How to Use This Calculator

Select known power or voltage and current as the calculation source.
Enter motor power, or enter voltage, current, and power factor.
Add motor efficiency to convert input power into shaft power.
Enter motor speed in revolutions per minute.
Use a reduction ratio of 1 when no gearbox is used.
Enter drivetrain efficiency for gearbox, belt, chain, or coupling loss.
Add a service factor for shock, starts, duty, or safety margin.
Press the calculate button and review the result above the form.

Example Data Table

Power	Motor Speed	Reduction Ratio	Drivetrain Efficiency	Output Speed	Estimated Output Torque
0.75 kW	1420 rpm	1:1	100%	1420 rpm	5.04 N·m
3.7 kW	1450 rpm	2:1	95%	725 rpm	46.30 N·m
10 hp	1760 rpm	5:1	90%	352 rpm	182.07 N·m

Understanding Motor Output Torque

Motor output torque tells how strongly a shaft can turn a load. It links power, speed, and losses into one useful value. Designers use it when selecting gearboxes, couplings, conveyors, pumps, fans, and rotating tools. A torque result is only meaningful when the input assumptions are clear. Speed, efficiency, power factor, and reduction ratio all change the final number.

Why Torque Matters

Power shows the rate of work. Torque shows twisting effort. A high speed motor can have modest torque at the motor shaft. After a reducer, the output speed drops, but torque usually rises. The rise is limited by gearbox efficiency. This calculator includes that loss, so the result is closer to a real shaft value.

Power Entry Choices

You may enter known power directly. You may also estimate power from voltage and current. For direct current, electrical power is voltage multiplied by current. For single phase alternating current, power factor is included. For three phase systems, the square root of three is also used. Efficiency then converts input electrical power into estimated mechanical power.

Reading the Result

The main result is output shaft torque in newton meters. Extra units are shown for field use. The design torque applies the service factor. Use that value when the load starts hard, stops often, or shocks the drive. Smooth fans may use a small factor. Crushers, lifts, and indexing machines need greater allowance.

Good Engineering Practice

Always compare calculated torque with rated equipment data. Motors have starting, pull up, breakdown, and continuous torque limits. Gear reducers also have thermal and mechanical ratings. Check duty cycle, ambient temperature, altitude, mounting position, lubrication, and overload protection. The calculator helps with planning, but nameplate data and manufacturer curves should guide final selection.

Common Use Cases

Use the tool during early sizing. It helps estimate conveyor pull, mixer drive needs, wheel drive torque, and pump shaft demand. It also helps compare motor speeds. If the same power runs at lower speed, torque increases. That simple relationship explains many drive choices. It also helps prevent weak couplings, undersized keys, and overloaded reducers. Document inputs, because small assumptions can change torque enough to affect cost, safety, maintenance, and service life during later reviews.

FAQs

What is motor output torque?

Motor output torque is the twisting force available at a rotating shaft. It depends on mechanical power and shaft speed. Lower speed gives more torque for the same power.

Should I enter input power or output power?

Use output power when you know rated mechanical power. Use input power when you only know electrical input. The calculator applies efficiency to convert input power into estimated shaft power.

How does gear ratio affect torque?

A reduction gearbox lowers output speed and increases torque. Real torque gain is reduced by drivetrain efficiency. A 3:1 reducer usually gives less than three times torque because losses exist.

Why is efficiency included?

Efficiency accounts for motor and drivetrain losses. Electrical input power is not fully converted into usable shaft power. Heat, friction, and magnetic losses reduce the available output torque.

What is service factor?

Service factor is a design multiplier. It adds margin for shock loads, frequent starts, jams, overloads, or harsh duty. Use manufacturer guidance for final equipment selection.

Can this calculator handle three phase motors?

Yes. Choose the voltage and current source option. Then select three phase AC. The calculator uses voltage, current, power factor, and efficiency to estimate motor output power.

Is running torque the same as starting torque?

No. Running torque is based on normal shaft speed and power. Starting torque depends on motor design, supply conditions, controls, and load inertia. Check motor curves for starting checks.

Can I save the calculation?

Yes. Use the CSV button for spreadsheet records. Use the PDF button for a simple report. Both downloads use the current form values and calculated results.