Blood accounts for 7% of the human body weight, with an average density of approximately 1060 kg/m 3, very close to pure water's density of 1000 kg/m 3. The average adult has a blood volume of roughly 5 litres (11 US pt), which is composed of plasma and several kinds of cells.bout 55% of blood is blood plasma, a fluid that is the blood's liquid medium, which by itself is straw-yellow in color. The blood plasma volume totals of 2.7–3.0 liters (2.8–3.2 quarts) in an average human.