The 70,000 bodysize is actually an average that assumes a 70kg average human, and a density of 1 kg/l, the same as water. You can think of bodysize as a measurement of volume in ml.

So basically, the BC is 300 times the volume of the average human.

2 meters, however, is not the right baseline measurement to use, as you want to find the average height of someone who weighs 70 kg, and 2 meters tall is unusually tall.

Using some google searches on height-weight charts, I'd say your 70kg person comes up being about 1.75 meters tall.

So, k should be 13061

I get roughly 11.53 meters height.

Now then, according to my own calculations, the size of a tile should be approximately 3m cube. This is based off of the fact that every z-level is capable of being a single "story" of a building, using roughly human creatures. (See here:

http://www.bay12forums.com/smf/index.php?topic=61215.0)

This makes a Bronze Collossus fit in a 4-meter tall stack of single tiles horizontally while standing fully upright. (Technically, it would spill out to the sides by a small amount, but this could be negligible.)

A single tile contains both infinitely large and infinitely small amounts of space, so your calculations are off.

By infinity.

This exists solely because of the ban on multi-tile creatures. It can be changed.