A magnetic reluctance flowmeter having a magnetic float in which a permanent magnet and soft iron pole pieces are arranged in such a manner that the resulting magnetic field passes directly through the yoke which is also made of soft iron. The shape of the yoke is such that, as the magnetic float is progressively displaced from its neutral position within the yoke, the magnetic field progressively saturates regions of the yoke causing some of this field to emanate into the space surrounding the yoke, in which locations this emanating field interacts with the magnetic field sensors in such a way as to modify the electrical signal produced by a sensing circuit.