The main goal of the Compressed Baryonic Matter (CBM) Experiment at FAIR is to probe the
QCD phase diagram at high net-baryon densities and moderate temperatures with nucleus-nucleus
collisions, in order to locate the possible first order phase transition from hadronic to partonic
matter and its critical end point (CEP). The higher moments (cumulants) of conserved quantities,
such as baryon number, strangeness and electrical charge, are suggested to be sensitive to the
proximity of the CEP. In order to assess the behavior of these cumulants, it is crucial to determine
the reaction volume. Different procedures for centrality selection, based on participant multiplicity
measured with the STS detector or on spectator multiplicity measured with the new FSD detector,
allow us to study reaction volume fluctuations and their impact on net-baryon cumulants. The
present work focuses on the first step to determine the reaction volume: exploring different
centrality determination procedures using the hadronic transport model SMASH.