It is well documented that much of the strength and hardness of nanostructured, carbide free bainitic steels come from the very small thickness of bainitic ferrite plates. In the current work, the Williamson-Hall method has been used to determine the bainitic ferrite plate thickness. The fitting of X-ray peaks to various functions showed good coefficient of determination values for Gaussian function compared to the Cauchy and Pseudo-Voigt functions. The thickness of bainitic ferrite plates was measured by distinguishing the contribution of very small plates on peak broadening from the lattice microstrain and instrumental effects. The results showed that by decreasing the transformation temperature the bainitic ferrite plate thickness decreases. The determined thicknesses were compared with that of measured from transmission electron microscope micrographs. There is a good qualitative and quantitative agreement between the thicknesses measured using both methods. (C) 2015 Elsevier B.V. All rights reserved.