The human population can be exposed to copper oxides used as plant protection products and feed additives. They are commercially distributed as powders, and limited information on their particle size distribution is available. The EFSA Guidance on Particle-Technical Requirements requires measuring the particle size distribution to assess whether a nano-specific risk assessment should be performed. To measure the particle size distribution using electron microscopy (EM), a dispersion protocol that aims at maximal de-agglomeration followed by on-grid sampling is evaluated.