We present characteristic ratios of the unperturbed dimensions C-r = (o)/n, where (o) is the mean-square unperturbed end-to-end distance and n is the number and (l(2)) is the mean-square length of the backbone bonds, calculated for poly(D-beta-hydroxybutyrate) (PHB) chains with traditional rotational isomeric state (RIS) models, a computer-generated RIS model, and molecular dynamics simulations of isolated PHB chains. These dimensions are compared with those reported in the literature for PHB observed in both dilute solutions (C-r similar to 8) and in the bulk melt (C-r similar to 40). The traditional and computer-generated RIS models yield C-r similar to 3-4, while C-r similar to 8 is obtained from the molecular dynamics simulation of isolated PHB chains. In addition we find that the dimensions calculated for PHB chains are independent of their stereosequence. A search for the occurrence and correlation of PHB repeat units adopting the crystalline helical conformation conducted during the molecular dynamics simulation failed to uncover the source for the unusually large dimensions (C-r similar to 40) reported for PHB chains in the amorphous bulk. We do observe, however, that the conformations of PHB repeat units are not totally independent of the conformations of neighboring repeat units, as would normally be expected for polyesters with rigid trans ester bonds. Nevertheless, we find PHB to be a conformationally diverse and flexible, randomly coiling polymer with dimensions not atypical for aliphatic polyesters, consistent with the behavior observed for PHB in dilute solution but not by SANS in the amorphous bulk.