  The centrality of heavy-ion collisions is directly related to the medium
created therein. A procedure to determine the centrality of collisions with the
LHCb detector is implemented for lead-lead collisions at
$\sqrt{s_{\scriptscriptstyle\text{NN}}}=5\, \mathrm{TeV}$ and lead-neon
fixed-target collisions at $\sqrt{s_{\scriptscriptstyle\text{NN}}}=69\,
\mathrm{GeV}$. The energy deposits in the electromagnetic calorimeter are used
to determine and define the centrality classes. The correspondence between the
number of participants and the centrality for the lead-lead collisions is in
good agreement with the correspondence found in other experiments, and the
centrality measurements for the lead-neon collisions presented here are the
first performed in fixed-target collisions at the LHC.
