The role of sample size in the estimation of geological strain, both finite strain (R-s) and that of the orientation of the finite strain ellipse (phi(s)), is investigated for clastic sedimentary rocks. This study looks at four strain methods, the Robin method, the linearization method, the Mutchrone and Meere method and the mean radial length method that are initially tested using simulated strained data sets and subsequently by applying the methods to real data. It is found that the optimum strain analysis sample size for a clastic sedimentary rock is primarily dependant on the intensity of strain suffered by that rock because of the error behavior associated with R-s estimates. An iterative process is therefore recommended starting with a minimum sample size of 150, which can be maintained or reduced based on the initial R-s estimates. (C) 2003 Elsevier Science Ltd. All rights reserved.