  The top quark is the heaviest elementary particle in the Standard Model (SM).
For this reason, a precise determination of its mass $m_t$ is part of the LHC
physics program. The most accurate determinations of $m_t$ rely on the
kinematic reconstruction of the top decay products and on the use of Monte
Carlo event generators. In these proceedings I discuss the impact of different
theoretical descriptions for the process of top pair production at the LHC on
the extraction of $m_t$.
