The production of controlled bacterial cellulose structures for various applications requires a better understanding on the mechanism of cellulose biosynthesis as well as proper tools for structural characterization of the materials. In this work, bacterial celluloses synthesized by an Asaia bogorensis strain known to produce fine cellulose fibrils and a commonly used Komagataeibacter xylinus strain were characterized using a comprehensive set of methods covering multiple levels of the hierarchical structure. FT-IR spectroscopy and x-ray diffraction were used to analyse the crystal structure and crystallite dimensions, whereas scanning and transmission electron microscopy, atomic force microscopy, and small-angle x-ray and neutron scattering were employed to obtain information on the higher-level fibrillar structures. All methods yielded results consistent with the A. bogorensis cellulose fibrils being thinner than the K. xylinus fibrils on both the level of individual cellulose microfibrils and bundles or ribbons thereof, even though the exact values determined for the lateral fibril dimensions depended slightly on the method and sample preparation. Particularly, the width of microfibril bundles determined by the microscopy methods differed due to shrinkage and preferred orientation caused by drying, whereas the microfibril diameter remained unaffected. The results were used to understand the biological origin of the differences between the two bacterial celluloses.