In situ bulk density modelling is fundamental to resource estimation, mine planning, geotechnical design, and reconciliation. Because density directly affects tonnage estimates, minor errors can significantly impact metal or product estimates. Industry standards such as the JORC Code require density to be treated with the same rigour as grade, including transparent documentation of sampling methods, porosity and moisture treatment. At Rio Tinto Kennecott’s Bingham Canyon Mine, recent innovations have improved density model accuracy through advanced measurement technologies and new workflows, including disciplined validation. The key developments include CoreLok® for dry bulk density in porous materials and the first operational deployment of downhole muon tomography in an active open pit. Combined with robust QA/QC and geostatistical modelling, these approaches deliver more representative and reliable models for mine planning and operational decision-making.