Calculations of the structures of cucurbit[n]urils (n = 5–8) and estimations of thermodynamic parameters of their formation are carried out using a high-performance program package PRIRODA at the density functional theory level using the PBE functional and DZ basis set optimized for this functional. Based on the calculated Gibbs free energies of the reaction of CB[n] formation, it is concluded that the CB[6] homolog slightly dominates among the other products of the synthesis.