Question: How much blood is needed by the brain?

Rebecca Dewey answered on 24 Jun 2015:

The brain needs a continual flow of fresh blood as this brings the much-needed oxygen and fuel for the braincells to work. We express this blood flow as millilitres of blood per 100g of brain tissue per minute. An average brain weighs about 1.2 kg, so 100g of brain tissue is about one twelfth of the whole brain. Grey matter (the cells that do the working out of stuff) should have about 70 ml/100g/min of blood, whereas White matter (the cells that carry messages from one part of the brain to another) only need about 20 ml/100g/min of blood.

So in a normal adult human, the brain sees about 750 millilitres of blood per minute. This is about 15% of what the heart pumps around the body.

The body holds about 5 litres of blood in total (depending on body size) so about 750 ml of this are in the brain at any one time.