The dynamics of a binary neutron stars merger is governed by physics under the most extreme conditions, including strong space–time curvature, ultrahigh matter densities, luminous neutrino emission, and the rapid amplification of the initial neutron star magnetic fields. Here, we systematically explore how sensitive the magnetic field evolution is to the total mass of the merging binary, to the mass ratio of its components, the stellar spins, and to the equation of state. For this purpose, we analyse 16 state-of-the-art general relativistic magnetohydrodynamics simulations that employ a subgrid-scale model to account for the unresolved small-scale turbulence. We find that strong and rapid amplification of the magnetic field to volume-averaged values of ∼1016 G in the high-density regions is a very robust outcome of a neutron star merger and this result is only marginally impacted by either mass, mass ratio, spin, or equation of state.