Powder flowability is affected by a number of particulate properties including particle size, surface area, and surface roughness. Surface irregularities play an important role in controlling powder flow properties. In the present work, a relationship was derived between the reactive fractal dimension - representing the fractallity of the part of the surface participating in particle-particle interactions during powder flow - and the initial increase in density of a powder bed during densification. The reactive and true textural fractal dimensions for a model system comprised of silicified microcrystalline cellulose particles were also experimentally obtained. The concept of the reactive fractal dimension was shown to be helpful for a comprehensive description of the powder densification process. It indicates how rapidly the active interparticulate area involved in particle-particle interactions grows with powder size reduction. It is suggested that the reactive fractal dimension can be used for describing powder flow behavior and to elucidate the sensitivity of powder flowability to particle size changes.