This contribution investigates the effects of horizontal mergers and acquisitions on the plant capacity utilisation of the Swedish district courts over the periods 2000-2017. More specifically, we empirically demonstrate the decomposition of input-oriented and output-oriented technical efficiency by incorporating several concepts of plant capacity utilisation. Moreover, we also explore the impact of convexity on input-oriented and output-oriented measures of plant capacity in the short-run scenario in an attempt to discover the potential rationale behind the merger wave. To the best of our knowledge, we are the first to assess horizontal mergers by employing plant capacity utilisation concepts. The results indicate that the horizontal mergers improve capacity utilisation. Furthermore, the nonconvex frontier method provides a more conservative estimate of plant capacity changes of this merger wave.