Welcome… How to calculate crystallite size and average crystallites size from XRD data The crystallite size, D, has been calculated by applying Scherrer’s equation as: D=kλ/βcos⁡θ Where k = shape factor λ= nm (X-ray wavelength β= half-width of the diffraction band (FWHM) (radians θ = Bragg- diffraction angle (peak position in radians