Mesenchymal stem/stromal cells (MSC) have shown their regenerative potential in vitro, in preclinical models and are increasingly used in clinical applications as well. For cell therapeutic applications, MSC must be isolated from their resident tissues. For the isolation of MSC from adipose tissue, more and more systems are entering the medical device market. During the automated or semi automated isolation procedures within these systems the cells are subjected to mechanical strain. In order to design devices that isolate intact, viable cells, optimizations with experimental methods or fluid flow simulations become necessary. These methods require the input of basic parameters like cell volumetric mass density. The determination of this parameter is not trivial and currently avalable methods are very elaborate, cost intensive and experimental and thus not readily available. With the introduced method we describe a user-friendly method for the determination of the volumetric mass density of cells like adMSC with a density meter and a cell counter. The method is based on the hypothesis of a linear relationship between the volumetric mass density of the cell suspension and the volumetric mass density, number and diameter of the cells in a cell suspension. The volumetric mass density of the cell suspension and its medium without any cells are measured. Cell number and cell diameter distribution are determined using a cell counter. From these values the volumetric mass density of the cells can be determined. The values calculated with the described method was compared to volumetric mass density evaluated using the standard method of density centrifugation. For cultured adMSC the determined a median volumetric mass density of 1,0525 g/cm3 using the proposed method and 1.045 g/cm3 using density centrifugation. Thus, both methods show only a 0,7% difference. The main advantage of our newly introduced method is the shorter time required to perform the measurements, the lower amount of cellular material needed in the process. Furthermore, the devices used are readily available on the market and thus easily accessible.