The speed a synchronous motor will run can be determined by the number of poles of the motor and the frequency of the electrical service using the formula:
RPM = Hz* (2 / poles) * 60
where
RPM = shaft rotation speed or revolutions per minute.
Hz = frequency or cycles/sec.
Poles = number of poles of your motor.
So, for example, if you have a 4 pole motor on 60 Hz then RPM=60*(2/4)*60=1800 rpm.
60Hz is the most common frequency in the US.
50Hz is the most common frequency outside the US.

Approximate Electrical Motor Speed (rpm)
No. Poles	Speed with Rated Load		onous Speed (no Load)
	60Hz	50Hz	60Hz	50Hz
2	3450	2850	3600	3000
4	1725	1425	1800	1500
6	1140	950	1200	1000
8	850	700	900	750