Three Phase Motor Torque Calculator

Calculator

Calculation method

Rated motor power

Power unit

Operating load

Actual motor speed

RPM

Line voltage

Line current

Power factor

Efficiency

Supply frequency

Motor poles

Service factor

Starting torque estimate

Formula Used

Torque from shaft power:

T = 9550 × P(kW) / RPM

Three phase electrical input power:

Pinput(kW) = 1.732 × VL × IL × PF / 1000

Estimated shaft power from electrical data:

Pshaft(kW) = Pinput × Efficiency / 100

Synchronous speed:

Ns = 120 × Frequency / Poles

Slip percentage:

Slip = (Ns - RPM) / Ns × 100

Torque conversion:

lb-ft = N·m × 0.737562149

How to Use This Calculator

Select the calculation method.
Use rated shaft power when motor output power is known.
Use electrical input when voltage and current are measured.
Enter actual running speed in RPM.
Add frequency and pole count to calculate slip.
Press the calculate button.
Review torque, shaft power, slip, and comparison values.
Download the result as CSV or PDF when needed.

Example Data Table

Motor Use	Power	Speed	Efficiency	Power Factor	Estimated Torque
Small conveyor	7.5 kW	1440 RPM	89%	0.84	49.74 N·m
Centrifugal pump	15 kW	1460 RPM	90%	0.86	98.12 N·m
Industrial fan	30 kW	1475 RPM	92%	0.88	194.24 N·m

Three Phase Motor Torque Guide

What Torque Means

Torque is the twisting force at the motor shaft. It shows how hard a motor can turn a load. In three phase systems, torque depends on shaft power and actual speed. It also depends on electrical input when shaft power is not known. This calculator connects both views. It helps compare nameplate data with measured site data. It also gives slip and synchronous speed. These values help detect overload, weak supply, or wrong speed assumptions.

Why Three Phase Data Matters

A three phase motor uses line voltage and line current. Real power also needs power factor and efficiency. Voltage alone does not show the output force. Current alone can be misleading during starts or heavy loads. The calculator estimates input power first. Then it applies efficiency to get shaft power. Finally, it divides shaft power by angular speed. The result is torque in newton meters. It also converts torque to pound feet for practical reference.

Using Results for Maintenance

A torque estimate can support pump, fan, compressor, and conveyor checks. Higher torque than expected can mean blocked flow, poor bearings, tight belts, or wrong gearing. Low torque can point to low voltage, bad power factor, or an undersized motor. Slip is also useful. Normal slip means the rotor runs slightly below synchronous speed. Excessive slip may show overload or motor heating. Negative slip usually means the entered speed is too high for the selected poles and frequency.

Good Input Practice

Use measured running current for a loaded motor. Use line to line voltage for standard three phase systems. Enter rated power when it is known. Use the electrical method when only voltage and current are available. Select horsepower, kilowatts, or watts carefully. Efficiency and power factor should be realistic. Nameplate values are best. For design work, add a service factor or margin. For critical machines, compare the result with manufacturer torque curves. This calculator is an estimating tool. It supports checks, but it does not replace motor testing, protection settings, or engineering review.

Keep records from each inspection. Trend changes over time. A steady trend is useful. A sudden change deserves attention. Check wiring, load, supply, and ventilation before changing motor size.

FAQs

What is torque in a three phase motor?

Torque is the turning force available at the motor shaft. It depends on shaft power and running speed. Higher power or lower speed usually gives higher torque.

Which speed should I enter?

Enter actual loaded shaft speed in RPM. Use nameplate full load speed when measured speed is not available. Avoid using synchronous speed as actual speed.

Can I use horsepower?

Yes. Select HP as the power unit. The calculator converts horsepower to kilowatts before applying the torque formula.

Why does efficiency matter?

Efficiency converts electrical input power into estimated shaft output power. A motor never converts all input power into useful mechanical output.

What is slip?

Slip is the difference between synchronous speed and actual rotor speed. It is normal in induction motors. High slip can suggest overload or supply problems.

What does service factor torque mean?

It estimates the torque level related to the entered service factor. It helps review extra load allowance, but it should not replace nameplate limits.

Why compare rating and electrical methods?

Comparison helps check whether measured electrical data agrees with expected shaft demand. A large difference may show wrong inputs, abnormal load, or poor motor condition.

Is this calculator suitable for starting torque?

It gives an estimate using a percentage of running torque. Real starting torque depends on motor design, starter type, voltage drop, and load inertia.