How to calculate RPM using frequency
If a motor has two poles it will rotate once per mains cycle. At 50 Hz this will be 50 x 60 = 3000 RPM.
If a motor has four poles it will rotate half a revolution per mains cycle. At 50 Hz this will be 50 x 60 / 2 = 1500 RPM.
If a motor has six poles it will rotate one third of a revolution per mains cycle. At 50 Hz this will be 50 x 60 / 3 = 1000 RPM.


This can be generalised as RPM = 120 x f / poles.

Therefore # of poles = 120 x f / RPM.

Since induction motors slip the full-load RPM will be somewhat less than the calculated speed. From the rating plate we can see that the min -1 (revolutions per minute) is 930 to 950 at 50 Hz. This is just below 1,000 RPM so it must be a six-pole motor.