The production of okra using seedlings is a practice increasingly used by farmers. However, this system still lacks further research involving substrates, tray types, cell volume, pest control and disease. For this it is important to determine the optimum size of the plots, in order to reduce the experimental errors and the expenses with the experiment. The objective of this work was to determine the optimum plot size for experiments involving okra seedlings produced in Styrofoam trays of 128 cells using different methods. The methods were the maximum curvature, the maximum curvature with bootstrap simulation and the maximum curvature of the coefficient of variation. The evaluated characteristics were aerial part height, stem diameter, aerial dry matter, root dry matter, total dry matter and quality of seedlings as measured by Dickson quality index. The results showed that the optimum plot size is different between the evaluated characteristics and for characteristics there is no significant difference in the optimum plot size between the three different methods. The optimum size for evaluating okra seedlings produced in Styrofoam trays of 128 cells is 10 seedlings per plot and is indicated the use of the maximum curvature method using a bootstrap simulation.