Calculator
Formula Used
Mechanical power method: T = P / ω
Speed conversion: ω = 2πN / 60
Common shortcut: T(N-m) = 9550 × P(kW) / N(rpm)
Three phase power: Pout = √3 × V × I × PF × η
Single phase power: Pout = V × I × PF × η
DC power: Pout = V × I × η
Force method: T = F × r
Gear output torque: Tout = Tmotor × ratio × gear efficiency
Design torque: Tdesign = Tout × service factor
How to Use This Calculator
Select the method that matches your available data.
Use power and speed when rated output power is known.
Use electrical methods when voltage and current are known.
Enter efficiency as a percentage, such as 90.
Enter power factor for AC motors when available.
Add gear ratio when a reducer or gearbox is used.
Use service factor for shock, starts, and overload margin.
Press calculate to show results above the form.
Use CSV or PDF buttons to save the current calculation.
Example Data Table
| Example | Input | Speed | Method | Approximate Torque |
|---|---|---|---|---|
| Small pump motor | 1.5 kW | 1450 rpm | Power and speed | 9.88 N-m |
| Industrial drive | 5 kW | 1450 rpm | Power and speed | 32.93 N-m |
| Three phase estimate | 400 V, 10 A, PF 0.85, 90% | 1450 rpm | Electrical input | 33.54 N-m |
| Lever load | 250 N at 0.2 m | Optional | Force and radius | 50 N-m |
Electric Motor Torque Planning
Why Torque Matters
Torque is one of the first values checked when selecting an electric motor. It tells how strongly the shaft can twist a load. Speed alone does not prove that a motor can start, lift, mix, cut, or move a machine. A small motor may spin fast, yet stall when load torque is high. A large motor may run slowly, but deliver strong turning effort.
Power and Speed Method
Power and speed are the common inputs. The calculator converts power to watts. It then converts speed to angular speed. Torque is found by dividing power by angular speed. This gives newton meters. The tool also shows pound feet and ounce inches for shop use.
Electrical Input Method
Electrical inputs are helpful when mechanical output power is unknown. Three phase motors use line voltage, current, power factor, and efficiency. Single phase motors use voltage, current, power factor, and efficiency. Direct current motors use voltage, current, and efficiency. These methods estimate output torque from electrical input power. Efficiency matters because losses turn part of input power into heat.
Gears, Service Factor, and Load Sharing
Gearboxes change torque and speed. A reduction gearbox raises output torque. It lowers output speed at the same time. Real gearboxes also lose energy. The gear efficiency field reduces the ideal torque. Service factor adds a safety margin for shock, starts, and uneven loads. Motor count divides the required load across shared drives.
Reading the Result
There are several ways to read the result. Motor torque is the torque at the motor shaft. Gear output torque is the estimated torque after the selected ratio. Design torque includes the service factor. Per motor torque helps when two or more motors share the same load. Always compare these values with continuous ratings, not only peak ratings. Check units carefully. A wrong speed unit or radius unit can create a large error. Keep a written record for review. Repeat the calculation when any design assumption changes later.
Practical Notes
Use realistic values before making decisions. Nameplate data is usually better than guesses. Rated torque is not the same as locked rotor torque. Starting torque, breakdown torque, duty cycle, cooling, voltage drop, and ambient heat can change the final choice. This calculator is useful for planning, comparison, and early sizing. Final motor selection should follow manufacturer data and local electrical rules.
FAQs
What is electric motor torque?
Electric motor torque is the twisting force produced at the shaft. It shows how much turning effort the motor can apply to a load.
What is the basic torque formula?
The common formula is T = P / ω. Power must be in watts. Angular speed must be in radians per second.
How do I calculate torque from kW and rpm?
Use T = 9550 × kW / rpm. This gives torque in newton meters for metric motor sizing.
Why is efficiency included?
Efficiency accounts for losses inside the motor. Not all electrical input power becomes shaft power. Some energy becomes heat.
What does power factor do?
Power factor adjusts AC electrical power. It is used for single phase and three phase motor estimates when measuring voltage and current.
Does a gearbox increase torque?
A reduction gearbox increases output torque. It also reduces output speed. Gear efficiency should be included because real gears have losses.
What is service factor?
Service factor is a sizing margin. It helps cover shock loads, frequent starts, uneven loading, and practical operating changes.
Can this replace manufacturer motor data?
No. Use it for planning and comparison. Always check nameplate values, torque curves, duty class, and manufacturer ratings before final selection.