Abstract The effect of small-scale heterogeneities on fluid flow through a reservoir is determined using one of so called mathematical upscaling methods, that as such are fairly well established. Less well established, however, are the operations that provide their input, i.e. construction of reservoir model and acquisition of data. We thereto propose systematic description of facies and bed and systematic data sampling. We upscale the ensuing model and data through a two-step flow simulation, i.e. first on the flow cell and then on the flow unit scale. This work provides for a straightforward and easily applicable upscaling method that incorporates the effects of all heterogeneities.