The leaf area determination is important in agronomic and physiological studies, as they provide information on the vegetable metabolism and methods used for this purpose should be accurate. In addition, agronomic trials as strategies for experimental precision can be improved by using plots with the appropriate dimensions and numbers of repetitions. The aims this study were: To develop a non-destructive model to estimate leaf area from two hybrid in bell pepper crop by using length, width and the relationship between length and width of leaves, when methods of leaf discs and ImageJ software are used; To create polynomial models for each hybrid; An integrated model with two hybrid; To evaluate the correlation between methods used; To determine the experimental plot size and number of replications to evaluate the yield, plant height, stem diameter and number of fruits per plant in bell pepper crop, cultivated in open-field with two irrigation depths, two irrigation frequency; a control without irrigation by modified maximum curvature method and linear response plateau model.