This study investigates the development of a scale-down approach for anaerobic digesters. Geometric similarity, flow regime, dimensionless cavern size and power consumption per unit volume (P/V) were identified as scaling criteria to design the pilot digester. At this pilot scale, a Computational Fluid Dynamics (CFD) model was validated using Particle Image Velocimetry (PIV) measurements and extended to the industrial anaerobic digester to describe its hydrodynamics and evaluate the robustness of the scaling criteria. The pilot scale CFD simulations were able to capture the main features of the flow, and model P/V and cavern diameter (Dc) with an average error of 4% and 3%, respectively. The comparison between the pilot and the industrial scale showed a deviation of 9% for P/V and about 5% for Dc and similar distributions of the dimensionless velocities inside the cavern, validating the scaling approach. •A scaled down approach to viscoplastic flows in anaerobic digesters was developed.•The numerical model was validated at pilot scale by Particle Image Velocimetry data.•The model was successfully applied to industrial scale to describe its hydrodynamics.•Constant Re, P/V and dimensionless cavern diameter were found to be robust criteria.