Polystyrene as an archetypal charge-stabilized colloid model system was used in this work under well de®ned preparation conditions. A continuous preparation technique was used to control the suspension parameters salt concentration c and particle number density n. Measurements of n were performed using both conductivity in the completely deionized state and static light scattering. We found a signi®cant deviation between the position of the ®rst maximum of the static structure factor q max 2p=L and an estimate identifying the relevant length scale L with the average inter-particle distance d Å n 71=3 . Instead, q max was observed to follow the relation q max (2.20 AE 0.03)p=d Å , which is equivalent to L (0.91 AE 0.02)d Å . Use of this led to consistent values for n in the crystalline and shear molten states and an improved precision in the ¯uid-like ordered state. Interestingly, q max of the ¯uid phases was further observed to be very close to the Bragg peak of the corresponding crystal phase which was determined by the nearest neighbour distance d NN . This supports the idea that the local structure of the strongly correlated ¯uid is very similar to that of the crystalline phase.