The unit of blood, cc, is milliliter, the unit of volume. That is, 1cc = 1ml. Generally the human blood will show a positive relationship with the body weight, the human blood will generally account for 7% to 8% of the human body weight. So the amount of blood contained in each person is different. When donating blood, it is often said that one unit of blood or two units of blood will be donated. One unit represents 200ml of blood and two units would represent 400ml of blood. In general, blood donation is usually one unit, i.e. 200ml of blood. You can’t donate blood on an empty stomach, and you should drink plenty of water before donating blood. Blood donation should go to a regular blood donation station to protect personal safety.