Available data regarding the nuclear halo candidates are systematically analysed in terms of the asymptotic normalization coefficients measured experimentally. On the other hand, we have put forth conditions for nuclear halo formation, and compared with the experimental data. Based on the analytical expressions of the expectation value for the operator r2 in a finite square well potential, we have presented the improved scaling laws for the dimensionless quantity / R2 of nuclear halo, which seem to be in reasonable agreement with the experimental data.