Biometric measurements from specimens from the calcareous nannofossil Hornibrookina were collected to help determine taxonomic and evolutionary relationships within the genus. Two sets of data are included. The first (Supplementary Data 1) are measurements taken from SEM microphotographs (published and previously unpublished) to determine the number and arrangement of the bars or bar-like structures found in the nannofossil central areas of different Hornibrookina species. The second (Supplementary Data 2) contains measurements from light microphotographs for all Hornibrookina species include coccolith length and width measured along the cardinal axes of the elliptical nannofossils. Additional measurements of the length and width of the central areas of specimens from the Hornibrookina teuriensis-H. edwardsi lineage were taken to compare this feature for its taxonomic significance. The specimens measure range in age from early Paleocene to early Eocene. Specimens are from various locations globally including the Coastal Plain of eastern United States (Maryland, Virginia, New Jersey), Tunisia, North Sea, New Zealand, South Atlantic (São Paulo Plateau), and the Southern Ocean (Maud Rise).