I'm a big guy, so maybe I have 12 pints of blood. But my weight isn't all muscle so I don't know how much blood it takes to feed me the oxygen I need. I thought it was around 8 pints, or 1 gallon in an average sized person, but I can't remember what the Red Cross said 51 years ago when I took basic first aid. I'm 62 now and suffering from a TBI, PTSD, and CRS (Can't Remember S**t). If you cut an artery you can bleed out in one minute flat. Luckily for people who are unfortunate enough to suffer traumatic amputations, the smooth muscles in arteries spasm and constrict. That doesn't stop the bleeding, but slows it down and usually gives the person time for first aid to be applied if anyone is there to do it, and for help to be called.