We identify and characterize surface features on the length scale 1-100 nm on a free equilibrated surface of amorphous polystyrene (in contact with air), from a combination of scanning force microscopy and coarse-grained polymer simulation techniques. By carrying out a lateral autocorrelation analysis of the experimental and simulated surface height profiles, we find characteristic length scales of structural organization of polymer chains depending on their molecular mass in the range 3.9 kg/mol to 9 Mg/mol. The lateral autocorrelation functions exhibit an initial exponential decay, which corresponds to a correlated arrangement of several monomer segments at the surface of the amorphous polymer, followed by one or more peaks. The same autocorrelation analysis of the surface height data is applied to the simulated data created for the same system with a lattice chain model. By combining evidence of simulation and experiment results, we deduce that a characteristic feature in the surface autocorrelation function has a length scale close to the radius of gyration over several decades of molecular weight. This study therefore opens up new ways of characterizing polymer surfaces and even observing the polymer radius of gyration directly.