In order to provide parameters that can be used to tailor the crystalline and supramolecular structures of pure polyhydroxybutyrate, we synthesized polymers with fractions of meso groups in the range 0.5-1. We confirmed the random polymerization of R and S enantiomers by the catalyst. From Xray diffractograms, the lattice parameters were determined; they remained constant for the observed range of fractions. We also traced the directional crystallite sizes over tacticity, which change significantly for one unit cell direction. The respective crystalline phase atom fractions were quantified by iteratively fitting amorphous phase diffraction patterns. We found that the crystalline contents of small-crystallite polyhydroxybutyrates have so far been underestimated. X-ray diffraction and transmission electron microscopical observations from polymers with meso group fractions of 0.5 are discussed. To facilitate the quantification of crystalline atom fractions, we refined two accessible infrared absorption spectroscopy-based indices. These indices, and the fundamental correlations between chemical and crystallite structuring reported herein, allow to tune structure-dependent properties, e.g., melting point and toughness, of mixed-tacticity polyhydroxybutyrates over wide ranges.