Pebble sizes in terms of their Stokes number and their physical size in the disc model of Bitsch et al. (2015a) as a function of time. The times are (top to bottom) 10⁴, 10⁵, 10⁶ and 10⁷ yr. The pebbles start their inward drift from the outermost point of the curves, indicating that they will grow as they drift inwards. The jump in the pebble sizes at ≈7 AU at t = 10⁴ and t = 10⁵ yr as well as at 1.5 AU at t = 10⁶ yr is caused by the transition at the water ice line, where we assume that the pebble flux reduces by 50% due to the evaporation of water ice. The sizes and Stokes numbers of the pebbles correspond to the nominal pebble flux marked by the solid red line in Fig. 1 and to the pebble surface densities marked by the black dotted lines in Fig. 2.