A scientific disparity exists on the question of how total knee arthroplasty (TKA) size and the main dimensions of a TKA affect wear on the tibial insert. Although some results have been presented about the existence of such a relationship, a closed-form mathematical description or approximate solution has not yet been delivered. This paper provides a numerical description of the influence of TKA size and TKA-related dimensionless parameters on tibial tray wear by means of multibody dynamics simulations (MBD) involving six commercially available, cruciate retained (CR) TKAs. Boundary- and initial conditions for the multibody dynamics simulations were set according to ISO 14243-1-2009 standards to facilitate comparison with experimental data found in the relevant literature. Results showed that all the investigated parameters have a critical level of impact on wear, and they can be predominantly approximated by linear functions. The specific TKA depth ratio (R² = 0.89) has the strongest effect by having the highest positive slope (40.27). This parameter is followed by the specific TKA volume ratio (R² = 0.77) with a relatively high positive slope (18.77). The third parameter in the rank is TKA size (R² = 0.99), where the effect on wear, based on its slope (1.59), is considerably lower. The specific TKA width ratio (R² = 0.91) was ranked as the fourth parameter, since, as a quadratic function, it has a peak, which also limits its maximum effect on wear. Therefore, this parameter was evaluated as the one with the least effect. These findings, together with the introduced dimensionless parameters, serve as practical design ratios, highlighting alternatives on how to enhance TKA wear performance and ensure minimal wear by optimal sizing.