A device that determines directly the force between two magnetic poles. A long magnet is balanced on a knife edge so that it takes up a horizontal position. One magnetic pole of a second long magnet is brought near to one end and the force (of attraction or repulsion) between the poles is balanced by the addition of weights or the action of a movable rider at the other end to restore the horizontal position. The magnets are made long in order to reduce interference by interaction between their second poles.

The magnetic balance can also be used to measure the strength of a magnetic field. In this type of balance the magnet that acts as the balance arm is replaced by a long conductor. A known current is passed through the conductor and the force exerted on one end by a pole of the magnet to be measured is balanced as above. The field due to the magnet may be calculated from the force between it and the known field due to the current. This type of balance can be calibrated to read magnetic field directly for a stated current and distance between the poles.

This method of measurement contains errors since the precise location of the magnetic poles is indeterminate. More accurate methods have been devised that measure the magnetic moment or magnetic flux density associated with permanent magnets and current-carrying conductors. See flip-coil; Cotton balance.