Orifices are largely used in pipeline systems. The most common application is to measure the discharge of the water flowing through. However, orifices may be used to adapt hydroelectric power plants submitted to moderate increase of installed generation capacity. For this application, the orifice is firstly characterized by a pair of head loss coefficients evaluated by a numerical simulation. Two different orifice shapes, chamfered and rounded orifices, were systematically studied in conduits with laboratory experiments. The main goal of the study is to evaluate the effects of orifice geometrical parameters on the head loss coefficients. A global empirical relationship has been found and can predict the head loss coefficients in both flow directions of a given orifice contrary to previous studies, which focused on sharp approach flow. These head loss coefficients depend on the inner diameter, thickness, inner thickness, chamfer angle and/or shape of orifices.