Cell volumes of phytoplankton collected from 12 different stations distributed in western and central Indian Sundarbans were estimated through calculation of similar type of geometric models. 12 geometric shapes have been assigned to calculate the cell volume of 47 phytoplankton species documented during the study period. The cell volume of the observed species was more in the western sector (112.89-269383.60 urn3) compared to the central sector (108.37-225131.20 urn3). Among 47 species recorded during December 2011, cell volumes of 6 species exhibited significant inverse relationships, and 2 species exhibited significant positive relationships with aquatic salinity. Our results suggest that cell volume of certain phytoplankton species can be used as indicator of aquatic salinity. © The National Academy of Sciences, India 2012.