Electrical - Motor

It is done at design stage >Normally IEC and BS specify limits as 600% of full load current subject to Tolerance which is 20%.So maximum starting current should be within 720% of rated current. Refer any motor manufacturers catalog where for each rating it is mentioned.Normally in 2 pole motors it is difficult to limit Starting current also known as Locked rotor current Or LRC.In India Consultants some times limit to 600% without tolerance which means its 500% with tolerance.In Boiler feed pump motors its normally restricted .There are cases where it has been restricted to 300% .But these are all special cases .The test certificate of manufacturer will give the actual value obtained during testing.No other method to calculate except you can have a facotor of 7.2Times FLC and arrive at LRC

I would probably use an amp meter and just measure it directly. An osciloscope that can lock the pattern at peak voltage would be helpful also.