Abstract: A flow conditioner comprising an apertured circular plate to be placed in a conduit in an orientation substantially perpendicular to the axis of the conduit. The apertures are circular and are arranged in a plurality of radially spaced circular arrays around a central aperture. The center of the central aperture and the centers of the circular arrays coincide with the center of the circular plate. The apertures in each circular array are equally spaced apart around the center of the plate, and all the apertures in any one circular array are of substantially the same diameter. The size and number of apertures are such that the impedance to flow presented by the plate increases with the radius on which a given array of apertures is arranged.