How Many People Would Have To Die?

[TheRealJoeFish]

Let's do a "napkin calculation." This can get us in the right range, give or take an order of magnitude.

Each human has, what, 6 liters or so of blood? Let's say this is 1 cubic foot (guessing based on the size of 2-liter and gallon bottles).

Let's say the flow of blood is like a stream (that is, bound on the edges), because if we just have a 200-mile-wide ocean of blood, we're all screwed (see, e.g., Blood Ocean, starring Dethklok). We'll call a horse's bridle 4 feet off the ground, and we'll say our stream is as high as it is deep. A weird stream, but, mysterious ways, right? We're just trying to simplify the calculations.

So, 1 foot of stream is going to be 4 feet wide and 4 feet high, meaning 16 cubic feet of blood. That's 16 people. Since there are 5,280 feet in a mile, we get about 84,000 people for one mile of stream (assuming everyone's completely exsanguinated, which seems very difficult to accomplish). 200 miles of stream equals, well... 16.4 million people, a little under the population of the Netherlands. This is, of course, for a tiny, odd, square-shaped stream.

If we figure the flow is more natural - that is, maybe, 4 feet high in the middle and 20 feet wide, tapering off to the edges, well, that multiplies things by 2.5, putting us up around 41 million. That's, roughly, Ukraine.