In this study we demonstrate the complementarity of transmission electron microscopy (TEM) and atom probe tomography (APT) in studying the early stages of phase decomposition in the age-hardening Al–Mg–Si alloy AA 6016. Samples are subjected to natural ageing at ambient temperature or artificial pre-ageing at elevated temperature in order to produce different types of atomic clusters and early stages of precipitation before age hardening commences. APT is utilized to detect clusters and identify their number density, size and compositions, whereas TEM is applied to analyse and quantify number density, sizes and types of the hardening precipitates during artificial ageing. Finally, the particle statistics derived by APT and/or TEM were utilized to predict the mechanical properties of the various samples and conditions analysed.