How much blood is in the human body?

The exact amount depends on body size, with larger adults carrying up to about 6 litres and a newborn baby only around 250 to 300 millilitres. Blood is about 55 percent plasma, a yellowish liquid of water, proteins and salts, and about 45 percent red blood cells, with smaller amounts of white blood cells and platelets. The heart pumps the whole supply around the body roughly once every minute at rest. A standard blood donation takes about 470 millilitres, and the body replaces the plasma within a day or two and the red cells within several weeks. Losing more than about 30 to 40 percent of blood volume can be life-threatening.