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Motor torque calculator: current, power and slip of an induction motor

Output torque, rated current, input power, synchronous speed, slip and starting current of a three-phase induction motor from its nameplate. Free.

  • Instant result
  • Formula and standards shown
  • On desktop and phone

Pre-filled example

A 15 kW four-pole motor on 400 V three-phase, power factor 0.85, efficiency 0.9, drawing 28 A at 1,460 rpm, with a starting current ratio of 7.

V
A
kW
Hz
rpm

Result

16.49kWInput power

Output power
14.84kW
Apparent power
19.40kVA
Reactive power
10.22 kvar
Rated current
28.30 A
Output torque
98.11 N·m
Synchronous speed
1,500 rpm
Slip
2.67 %
Direct-on-line start
198.1 A
Star-delta start
66.0 A
Attach this calculation to a work order

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Motor figures pre-filled from the asset nameplate

Here, the calculator is free and the result is gone when you close the page. In Reglova, it is attached to the work order on the right machine: you find it again at the next breakdown, and on audit day.

The CMMS software comparison, our gaps included
  • Attached to the work order with its inputs: the server recalculates it, it stays verifiable.
  • On the technician's phone, even without a network.
  • In the machine's history, for the next breakdown.
  • The asset's nameplate data pre-fills the calculation.
Try the demoJoin the free beta
Reglova · Calculations · Work order WO-AT01-04219
Silent video, 33 s: from the work order for an oil leak on a shear cylinder, the tightening torque of an M12 bolt, then "Attach to the work order". A step to tighten it to 93.1 N·m lands in the checklist (step text from the French demo data). Watch the video

When to calculate motor torque and current

  1. 01

    Compare the current measured with a clamp meter with the rated current to spot an overload.

  2. 02

    Find the torque of a motor with an incomplete nameplate.

  3. 03

    Choose a protective device taking the starting current into account.

Good to know

On a variable frequency drive, the power factor and frequency read on the supply side no longer represent the motor: the calculator flags it.

Induction motor formulas: power, current, torque, slip

From the nameplate (voltage, power factor, efficiency, rated output) and a current or speed measurement, the calculator gives the input, output, apparent and reactive power, the rated current, the output torque, the synchronous speed, the slip, and the direct-on-line and star-delta starting currents.

Formula · Reference documents

Pin = √3·U·I·cos φ ; Pout = η·Pin ; In = Pout/(√3·U·cos φ·η) ; ns = 120·f/2p ; s = (ns − n)/ns ; T = Pout/(2π·n/60)

IEC 60034-1

Inputs and accepted ranges
InputUnitAccepted rangeExample
Supply2 optionsThree-phase
VoltageV1 to 20,000400 V
Measured currentA0.01 to 100,00028 A
Power factor cos φ0.01 to 10.85
Efficiency η0.01 to 10.9
Rated output (nameplate)kW0.001 to 100,00015 kW
FrequencyHz1 to 40050 Hz
Number of poles2 to 484
Measured speedrpm1 to 100,0001,460 rpm
Starting current ratio Id/In1 to 157
On a driveYes / NoNo
Calculated results
  • Input powerkW
  • Output powerkW
  • Apparent powerkVA
  • Reactive powerkvar
  • Rated currentA
  • Output torqueN·m
  • Synchronous speedrpm
  • Slip%
  • Direct-on-line startA
  • Star-delta startA
What the calculator flags
  • Slip outside 0 to 10%: check the number of poles or the speed.
  • On a drive, power factor and frequency are not representative.

Every motor on site with its nameplate and history

  • Breakdowns reported by QR code
  • Work orders on the phone, even without a network
  • Mandatory inspections reminded by email
  • Audit file as a PDF, in one click
Try the demoJoin the free beta

Free during the beta, no credit card