Blood volume is the volume of blood (both red blood cells and plasma) in the circulatory system of any individual.
A typical adult has a blood volume of approximately 5 liters, with females generally having less blood volume than males. Blood volume is regulated by the kidneys.
Blood volume (BV) can be calculated given the hematocrit (HC; the fraction of blood that is red blood cells) and plasma volume (PV):
Blood volume measurement is indicated for the diagnosis and treatment patients suffering from congestive heart failure, chronic hypertension, renal failure and critical care.
The table at right shows circulating blood volumes, given as volume per kilogram, for healthy adults of a selection of animals. However, it can be 15% less in obese and old animals.