We relate the information about interfacial roughness in multilayers obtained by X-ray reflectometry in the low angle regime to what can be determined from cross-section images taken in a transmission electron microscope (TEM). The interfacial root mean square (rms) roughness for each individual layer can be derived from X-ray reflectometry in specular geometry in Co/Cu multilayer systems. The results are both qualitatively and quantitatively in agreement with results obtained by evaluating cross-section TEM images. Utilising non-specular scans in X-ray reflectometry gives additional details about the growth structure. In Co1-xZrx/Cu multilayers we suggest to correlate the Hurst parameter to the grain structure determined by cross-sectional TEM.