A dimensionally consistent size–strain plot method for crystallite size and microstrain estimation

X-ray diffraction (XRD) peak broadening analysis remains a cornerstone for quantifying crystallite size and lattice microstrain in materials. Among various approaches, the Size–Strain Plot (SSP) method is widely employed for its conceptual simplicity and ease of use. However, this study reveals that the equation most commonly applied in SSP analysis is dimensionally inconsistent—a critical flaw that has gone largely unnoticed and replicated across decades of materials research. This pervasive error raises concerns about the validity of a significant body of published microstructural data. By tracing the historical origin of the misformulated equation, we demonstrate how a seemingly minor oversight evolved into a widely accepted standard practice within the field. We then present a dimensionally consistent formulation that restores physical meaning and analytical reliability to the SSP method. The corrected framework re-establishes the SSP approach as a robust and physically valid tool for XRD-based microstructural characterization. • Identifies and traces the origin of a dimensionally inconsistent SSP formulation. • Demonstrates how omission of 1/ λ led to a widely adopted but non-physical equation. • Shows that the misformulated SSP equation has affected size–strain analysis for almost a decade. • Restores a dimensionally consistent SSP relation and rigor in XRD line-profile analysis, improving microstructural characterization. • Reveals how the same underlying method has been presented under two different names in the literature.