Abstract. The present work concerns a numerical investigation of the effect of orifice meter diameters on the discharge coefficient for flow measurement purpose. The flow is subject to two disturbers namely a 90° double bend in perpendicular planes and a 50% closed valve. The turbulent flow is examined in conduit with an inner diameter of D=100mm. The diameter of orifice meters are respectively d=40, 50, 60, 70 and 75mm which done for β ratio d/D respectively the values of 0.4, 0.5, 0.6, 0.7 and 0.75. The orifice meters are located in conduit at different stations downstream the disturbers. The flow is examined with air at Reynolds number Re=2.5x10 5 . The software used for this simulation is CFD code Fluent with k-ε like turbulence model. As a conclusion, the analysis of numerical results shows that when the diameter of the orifice meter increases the shifts deviation in the discharge coefficient increases this causes a great error in flow measurement. Contrary, when the diameter of the orifice meter decreases the shifts deviation in the discharge coefficient decreases and the errors in flow measurement is reduced. These results are the same with the two disturbers used separately in conduit.