Cylindrical weirs are one of the most commonly employed hydraulic structures to measure flow, compare to other types of the same width they pass larger discharge. This paper presents an experimental work together with a CFD simulation to study the effects of the geometric characteristics of a cylindrical weir and a ramp placed upstream or downstream of the same weir on the discharge coefficient. Three different weir diameters and three ramp angles under three different discharges were utilized. The results show that the geometric characteristics represented by the diameter of the weir affects the discharge coefficient when there is no ramp. The discharge coefficient was observed to decrease as the slope of the upstream ramp was increased, however as the slope of the downstream ramp was increased the discharge coefficient was noted to increase. A mathematical relationship was developed in order to calculate the discharge of flow passes over the cylindrical weir depending on its diameter.