Photocatalysis with TiO2 is one of the most promising methods for combatting environmental pollution. Of commercially available photocatalysts, Evonik Aeroxide (formerly Degussa) P25® titania is probably the most extensively used. In this communication, we quantitatively characterise the full phase composition (both crystalline and amorphous content) of P25®, as well as the microstructure of individual phases (crystalline domain size distribution and dislocation density). This was achieved with advanced X-ray diffraction (XRD) methods: Rietveld-RIR and whole powder pattern modelling (WPPM). Quantitative phase analysis (QPA) showed the precise composition of P25 to be 76.3wt% anatase, 10.6wt% rutile and 13.0wt% amorphous, and microstructural details are given for the two crystalline phases. •First time fully quantitative X-ray characterisation of Evonik Aeroxide TiO2 P25®.•P25® composed of 76.3wt% anatase, 10.6wt% rutile, and 13.0wt% amorphous phase.•Anatase phase had an average crystalline domain size of 15.5nm.•Rutile phase had a larger average crystalline domain size of 19.3nm.