[HartleyMBaldwin]

As you increase all dimensions of a solid equally, the surface and cross-sectional areas increase as the square of the dimensional increase, and the volume increases as the cube. Thus a 12-foot-tall human’s weight would be 8 times that of a 6-foot human having the same proportions.

[amorphous]

But humanoids aren’t square, they’re more cylindrical. :-)

[dainbramaged]

Thus a 12-foot-tall human’s weight would be 8 times that of a 6-foot human
The stories I've read about the "Kandahar Giant" claim he weighed around 1100 pounds after our guys blasted him down with hot lead and he stunk to high heaven. They put him on a pallet carried off by a Chinook helicopter. Is it true? I'm not sure.

[steve86]

“Thus a 12-foot-tall human’s weight would be 8 times that of a 6-foot human having the same proportions.”

I sure don’t weigh 8 times what a child half my height weighs. Not even four.