Relative weight (Wr) is an important and commonly used condition index that provides a measure of the well-being of a fish population by comparing the actual weight of a specimen with the ideal weight of a specimen of the same species and of the same length in good physiological condition, i.e. the standard weight (Ws). Two methods of calculating the standard weight are proposed in the literature: the RLP method and the EmP method. The aim of this study was to develop a standard weight equation for European perch by means of both methods, using length–weight data from 64 913 fish from 18 countries (across Europe and Oceania). The resulting equations were: log10 (Ws) = −3.1483 + 1.2663 log10 (TL) + 0.4291 [log10 (TL)]2 for the EmP method and log10 (Ws) = −5.3493 + 3.2152 log10 (TL) for the RLP method. The applicable length-range of the two Ws equations was restricted to 80–460 mm. A further research aim was to compare the performances of RLP and EmP. The resulting quadratic EmP Ws equation did not exhibit length-related biases, which suggests that it can be used to compute relative weight for European perch.