Mass losses during peeling and size sorting of cut strips in French-fries production are heavily influenced by potato size and shape. In this study the number of tubers per kilogram (N) is used as a raw material parameter to estimate the average principal dimensions, volume, surface area and specific surface area of potato tubers. A method called 'numerical shell' was developed to estimate the surface area of ellipsoid bodies. This method can be used for other three-dimensional objects as well when the analytical surface area equation is not applicable. The study is focused on Solanum tuberosum L. cv.: Agria, Asterix and Bintje. The paper outlines also the relationship between production yield and number of tubers per kilogram. It was shown that the peel losses and Specific Surface area increase proportional by N-1/3. Mass losses due to sliver removal increase linearly proportional with N. (C) 2003 Elsevier Ltd. All rights reserved.