Originally developed to determine the volume of red blood cells in blood, packed cell volume (PCV) measurements have more recently been used also to determine the volume of cells in tissue culture experiments. For blood, PCV is proportional to cell volume as determined using the Coulter principle, which relates particle volume to the change in electrical impedance as the particle passes through an aperture. However, this assumption has not been tested for the diverse cell lines used in cell culture. We compared PCV with Coulter counter-based cell volume measurements for five cell lines and found that standard PCV protocols comparatively overestimate cell volume compared to Coulter-based measurements. We hypothesize that this discrepancy is related to incomplete cell packing and demonstrate that it can be mitigated in some cells using fast and prolonged centrifugation.