We’ve calculated it could travel 17,000 kilometres (10,563 miles) in a week. The average adult has five litres (1.3 gallons) of blood pumping around their body. About 20 per cent of this blood is in the heart and arteries, whooshing out through the aorta at 45 centimetres (17.7 inches) per second for a person at rest. It reaches lows of just 0.5 millimetres (0.02 inches) per second as it branches out into the maze of tiny capillaries which deliver oxygen to cells, tissues and organs. The blood picks up speed again to around 25 centimetres (9.8 inches) per second as it returns to the heart in larger veins. Using these figures, you could calculate that the average speed of blood in the body is 28 centimetres (11 inches) per second, which equals about 17,000 kilometres (10,563 miles) in a week. The reality is far more complicated as blood pressure and heart rate (linked to how active you are, among other factors) affect blood velocity dramatically.
Answered by Alex Cheung.