Linear measurements of 31 Southern Ocean diatom species or genus groupings are presented and used in the derivation of species-specific biovolume, biomass and surface to volume ratios. Species measurements are in tune with summarised values in the literature and range from 2.6 to 2296 pm in length and 8.5 to 140 pm in diameter. Average cell volume ranged from 63 to 1.43 x 105 mu m(3) and biomass from 10 to 3686 pg C cell(-1), the values being smallest in pennate shaped species and greatest in cylindrical centrics. The 31 species can be divided into 7 small, 12 intermediate and 12 large biomass contributors based on their cell volume and/or their surface to volume ratio. Carbon biomass estimates from biovolume equations are discussed and suggest that future work including large Southern Ocean species is warranted. Species-specific biomass values reported here should serve as a baseline for future analyses of major diatom carbon contributors in the generally high nutrient, low chlorophyll Southern Ocean.