How many transfusion services multiply by the density of blood products to determine the volumes, particularly for aliquots (but also if you calculate actual volumes of units)? The Tech Manual states the specific gravity of RBCs as 1.100 but is that the packed red cell mass, not an adsol unit of RBCs? It also states the s.g. of apheresis RBCs in additive solution as 1.06. So what is the density of an adsol unit that is not apheresis? Can we assume it is the same? How close to 1.00 before it isn't worth doing the calculations? The TM lists the specific gravity of apheresis plts as 1.03. Is that close enough to 1.00 that we need not calculate for plts? There is some inherent slop in the calculations anyway because we don't measure the exact weight of that individual emply bag with however many segments and labels are attached. When we make aliquots we add an extra 5 ml of product for waste in the infusion tubing. At what point is it important to calculate and when can we assume that "weight equals volume" is close enough?