Dominant particle size, as function of orbital distance and time. Black lines represent the particle size expressed by the Stokes number, the dimensionless friction time of the particle (labels correspond to the disc age in yr). Yellow lines give the particle size in cm assuming the Epstein regime (10³ and 10⁷ yr omitted for clarity). Particle sizes decrease at wider orbits and at later times, but typically remain in the mm-cm regime in the giant planet formation zone (5−50 AU). Pebbles are spread to the orbital location where dust is still growing to pebble sizes r_g. Beyond this orbit most of the solid mass will be in smaller dust particles. The disc dissipation time scale was set to τ_dis = 3 Myr.