How much blood is in the human body?

An average adult has about 5 litres of blood, roughly 7% of body weight, so a 70 kg person carries about 4.9 litres. Women average a little less than men. At rest the heart pushes the whole volume round about once a minute; during hard exercise, cardiac output can rise fivefold.

Source: Hall & Hall, Guyton and Hall Textbook of Medical Physiology (14th ed., 2020)