The concepts of particle packing and water/paste layer theory are commonly used for basis of concrete mix design models. While particle packing insists on achieving fewer voids in aggregate matrix by adding fine aggregate, water/paste layer theories state that increasing the amount of fines will lead to higher water demand since the specific surface area of particles will increase. In order to calculate the thickness of excess paste, it is essential to quantify the shape of particles. However, there are uncertainties regarding how the various shape parameters would affect the packing and specific surface, mainly because up to now many of the shape parameters are not yet clearly defined and there are no commonly accepted methods for their measurement. In addition, the term “shape” needs to be defined, some research suggest that for obtaining an appropriate shape factor several parameters need to be measured e.g. flakiness, elongation, sphericity, convexity etc. The paper aims to derive a shape factor based on variation of packing from the packing of ideal spheres with the same particle size distribution as the studied aggregate and to apply the shape factor to calculate an approximate specific surface area value.