The authors report on critical dimension metrology on nanoscale gratings by means of laboratory-based spectroscopic reflectometry in the extreme ultraviolet (EUV). EUV reflectivity spectra of nanoscale gratings under grazing incidence illumination and their dependency on the geometrical grating parameters are discussed. A laboratory-based setup to measure such spectra is introduced and its main features are presented. A nanoscale grating with a grating period below 100 nm, consisting of multiple nanometer-size layers of materials, is experimentally investigated in the setup. The experimental results are consequently compared to a rigorous model fit of the reflectivity and thus the ability to model the grating’s interaction with EUV radiation is shown.