Critical dimension small angle X-ray scattering (CD-SAXS) is a metrology platform capable of measuring the average cross section and line width roughness (LWR) with a sub-nm precision in test patterns with line widths ranging from 10 to 500 nm. The X-ray diffraction intensities from a collimated X-ray beam of sub-Angstrom wavelength were collected and analyzed to determine line width, pitch, sidewall angle, LWR, and others structural parameters. The capabilities of lab-scale and synchrotron-based CD-SAXS tools for LWR characterization were tested by measuring a set of identical patterns with designed roughness amplitude and frequency. These test patterns were fabricated using EUV lithography with sub-50 nm linewidths. To compensate for the limited photon flux from the lab-based X-ray source, the incident beam of the lab system was collimated to a less extent than the synchrotron beam-based tool. Consequently, additional desmearing is needed to extract information from data obtained from lab-based equipment. We report the weighted nonlinear least-squares algorithm developed for this purpose, in addiiton to a comparison between the results obtained from our lab system and the synchrotron beam-based tool.