We investigate the distribution of local minima in the potential-energy landscape of metals. The density of energy minima is calculated for Na by using a pair-potential method to quench from stochastic configurations for system sizes ranging from 1 to 4000 atoms. We find a minimum system size, approximately 150 atoms, above which the density of energy minima is dominated by one sharp peak. As the system size is increased, the peak position converges to an asymptotic value and its width converges to zero. The findings of the pair-potential method for Na are confirmed by first-principles calculations of amorphous Al and V. Finally we present an example in which our results are applied to the complex bulk metallic glass Zr52.5Cu17.9Ni14.6Al10Ti5 (Vitreloy 105). The calculated density and bulk modulus of the Vitreloy are in good agreement with experiments. The analysis presented here shows that the thermodynamic limit is better described by one large supercell calculation than by an average over many smaller supercell calculations. We argue that the minimum cell size that is needed to accurately perform such a large supercell calculation for metallic glasses is about 150 atoms.