The advent of high‐resolution and high‐accuracy DEMs from photogrammetry and LiDAR is providing an invaluable tool to measure erosion/deposition. At this resolution, it is thus now essential to take into account soils’ bulk density variations. From a set of experiments in the Hiru‐dani experimental watershed, the authors propose a SfM‐MVS method to measure soil density. From a set of photographs prior‐and post‐excavation, we can calculate the volume and measure the mass of the material, deriving bulk‐density and other geotechnical parameters. The method has two main strengths: (1) it allows for site‐specific error analysis and (2) it works on unconsolidated heterometric material. In the Hiru‐dani, the bulk density of the eroded bedrock was twice the one of the forest soil and 0.4 higher than the debris‐flow deposit, showing that comparing DEMs is not sufficient to precisely account for soil loss erosion, or define the volume that was transported away from the catchment.