  Using a dedicated data sample taken in 2018 on the $J/\psi$ peak, we perform
a detailed study of the trigger efficiencies of the BESIII detector. The
efficiencies are determined from three representative physics processes, namely
Bhabha-scattering, dimuon production and generic hadronic events with charged
particles. The combined efficiency of all active triggers approaches $100\%$ in
most cases with uncertainties small enough as not to affect most physics
analyses.
