Assessment of crystallite size and strain of CaCu₃Ti₄O₁₂ (CCTO) with multimodal crystallite size is relatively a challenging task. Various estimation methods (Debye–Scherrer, Williamson–Hall, Rietveld refinement and Variance) are usually gave variation results due to different parameter selections of peaks broadening, for example, average line and integral breath (average and total). The high accuracy of estimation method is essential in order to obtain the best estimated result as close as possible to the observed crystallite size. Therefore, this Letter presents the comparison of estimation methods in determining the crystalline size and strain of CCTO from XRD peak broadening. The result shows that each method gave a different crystallite size as far as various solutions are concern and also depicts that the strain is same. However, Rietveld refinement, Debye–Scherrer and variance methods showed a highly correlated with domain size as observed from transmission electron microscopy analysis, due to an exclusion of the instrumental errors.