Accurate flow measurement is essential for the management of any type of fluid system. This research investigated the effect on accuracy that five types of 12-in. differential-pressure flow meters have as a result of being installed in pipelines of differing inside diameter. The types of meters chosen for this research were the classical Venturi meter, Halmi Venturi Tube, wedge meter, V-cone meter, and the X-meter. Each meter was tested for accuracy with 10 pipe wall offsets varying from a 0.125-in. sudden contraction to a 0.937-in. sudden expansion of the pipe radius. The meters' reading during each test series was compared with the meters' reading with no pipe wall offset at the same Reynolds number. This research demonstrated that for accurate flow measurement, most flow meters require that the inside diameter of the piping be the same as the inside diameter of the meter.