Differential number counts normalised to the Euclidean slope of the SPRITZ simulated galaxies in the mid- and far-IR with high-redshift extrapolation k_Φ = −1 (Eq. (2), solid black line). The shaded regions show the uncertainties due to the high-z extrapolation and 1σ errors of the LFs and GSMF used to generate simulated galaxies. Several observed values present in the literature are also shown (Papovich et al. 2004; Le Floc’h et al. 2009; Clements et al. 2010; Berta et al. 2011; Béthermin et al. 2012, 2020; Pearson et al. 2012; Geach et al. 2013; Magnelli et al. 2013; Murata et al. 2014; Hsu et al. 2016; Valiante et al. 2016; Davidge et al. 2017; Geach et al. 2017; Wang et al. 2017; Zavala et al. 2017; Stach et al. 2018). The thin coloured lines represent the normalised number counts for the different galaxy populations considered in SPRITZ: spirals (light green line), SBs (cyan line), SF-AGN (dark-green line), SB-AGN (orange line), AGN type-1 (blue line), AGN type-2 (magenta line), elliptical galaxies (red line), and irregular galaxies (brown line).