In the context of fertiliser centrifugal spreading, numerous mechanical models demonstrate that the acceleration on the spinning disc depends on the friction coefficient of the fertiliser against the vane. Nevertheless, when the dynamic friction coefficient is measured with traditional methods, the values do not reflect the fertiliser behaviour differences. In this study, the friction coefficient of the fertiliser is deduced from a mechanical model of the motion of the particles on a spinning disc which requires the measurement of the outlet angle of the particles (i.e. when they leave the disc). The outlet angle is extracted from an image of the fertiliser particle trajectories in the vicinity of the spinning disc. Values obtained for three fertilisers (ammonium nitrate, NPK and KCl) are compared. The influence of the disc configuration, the vane profile and the rotational speed is addressed. Results demonstrate that the method can be used to obtain a relative classification of fertilisers. We suggest to call equivalent friction coefficient the value obtained with this method since it corresponds to the dynamic friction coefficient of a fictive single particle which would have a pure-sliding motion on the vane and which would have the same behaviour that the real fertiliser particles regarding the ejection. This paves the way to establish a normalized method in order to perform a fertiliser typology with respect to real spreading behaviour.