Publications on magnetocaloric materials, magnetic refrigerators, magnetic heat pumps and magnetic power conversion machines contain experimental results as well as solutions obtained by physical modelling, analytical and numerical calculations. Whereas material scientists usually aim for physical property data, thermal and electrical engineers are interested in the efficiency of the operation and economists in both, production and operation costs of a machine. However, without exact data of the magnetocaloric and magnetic materials, no precise determination of the energy consumption of a magnetic refrigerator can be achieved. Magnetic and thermodynamic measurement techniques must be reviewed and discussed. In the article, a method for an accurate determination of a global COP of a magnetic refrigerator, heat pump, respectively energy conversion machine is proposed, taking all possible losses of the machines into consideration. Only a full account in a machine characterization gives the possibility to estimate correctly its final energy consumption. For a fair comparison of different magnetic refrigerators, a standardization of the COP and cost determination is very much required. The Working Party for Magnetic Refrigeration of the International Institute of Refrigeration aims to coordinate such an activity. This article is a first proposal and recommendation in this direction and shall serve as a basis for further discussions and improvements.