The oscillating water column is one of the most tested and used wave energy converter types. It requires the use of an air turbine connected to an electrical generator. The deep understanding of all physical quantities of the energy chain components is based on transducers. The electrical generator efficiency is a key input to wave-to-wire numerical models for wave energy conversion to enable the industry to embark on projects with reliable data. Assembly of a standard torque meter is not feasible in prototypes following an industrial design. Therefore, the turbine shaft power must be calculated from the electrical generator dry-testing results at various rotational speeds and loads. This paper presents normalised data for estimating generator power output and turbine torque based on generator efficiency measurements. Experimental results show the electrical generator efficiency dependency on the rotational speed and load. A new kind of filter to post-process the raw data was used. The results will be used as a reference for wave-to-wire numerical models of oscillating water columns and post-processing the data from prototypes operating in real sea state conditions.