Since 2010, a lot of progress was done concerning Small Angle X-ray Scattering (SAXS) extraction capabilities for dimensional control of line gratings. In this paper, we summarize the general methodology, including transmission (T-)SAXS experimental setup, and extract the line shape and roughness in line gratings. We describe step by step the full data treatment to extract the pitch, critical dimension (CD), line shape and roughness, focusing on the Line Width Roughness (LWR) extraction through a Power Spectral Density (PSD) analysis. The reliability of the extraction by T-SAXS is evaluated thanks to different extractions, comparison to TEM cross-section and analyses of count statistic in case of line roughness.