X-ray reflectivity (XRR) is often used to estimate the interface roughness. In principle, XRR can measure both surface and interface roughness. However, the sensitivity to the interface roughness is rather poor compared with the surface roughness. In order to improve the accuracy in the interface roughness, a combination analysis of XRR with high-resolution Rutherford backscattering spectroscopy was performed. The surface and interface roughness were determined so that both XRR and high-resolution Rutherford backscattering spectroscopy spectra can be reproduced. We also found that the effective roughness measured by XRR may depend on the angle of incidence. This is because the roughness depends on the size of the probing area. Copyright (c) 2014 John Wiley & Sons, Ltd.