Thickness-dependent ordering of lamellar microdomains in symmetric polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) thin films was studied using scanning force microscopy (SFM), scanning electron microscopy (SEM), and grazing incidence small-angle X-ray scattering (GISAXS). The extent of perpendicular orientation for the lamellar microdomains on a neutral substrate was assessed at various film thicknesses around a lamella period (1L(0)) by varying the molecular weight of PS-b-PMMAs. The lateral ordering of perpendicularly oriented lamellae was evaluated with the defect distance (D) and orientational correlation length (xi) to extract the power law relationships with film thicknesses. The lateral ordering of higher-molecular-weight (>74 kg/mol) PS-b-PMMA films is enhanced by increasing film thickness, whereas in a low-molecular-weight (50 kg/mol) PS-b-PMMA, it is enhanced by decreasing film thickness below 1L(0). (C) 2015 Elsevier Ltd. All rights reserved.