Blocking facies information to a constant length prior to three-dimensional (3D) modelling is necessary with current 3D geostatistical modelling techniques. The high-resolution information from core and well logging must be upscaled to unify the scale to a target scale considered in building the 3D numerical models. A downside is the inevitable loss of information when the majority facies is assigned to each upscaled interval. The loss of such information could become problematic when dealing with small shale barriers in the middle of the reservoir or at the boundary of the facies transitions. This paper addresses the information loss by retaining as much information as possible in the upscaling process and proposes a metric to account for small-scale information that is mixed during the process: such a metric is referred to as facies mixing measure (FMM). Retaining more information in the upscaling process and utilizing that information to better model petrophysical properties is an important contribution. FMM is calculated during the upscaling step and is treated as a secondary property during petrophysical property modelling. Cross-validation with two different datasets demonstrates improvements in porosity estimation.