Magnetic field calculations for a magnetic stirrer and motor

hamshie.k

i am building a magnetic stirrer. one magnet is placed inside the fliud for rotation.

another magnet is affixed in the motor.

i need calculations for the force between these permanent magnets. I have to find that the force created by this magnet had the ability to rotate the fluid. please suggest me all the calculations??

If possible suggest me the selection of motor??