Human giants are physically impossible, because when a body is scaled up, its weight grows as the cube while bone strength only grows as the square, so the body crushes itself.

Legend says giants could grab men and sheep in one hand, climb beanstalks to a castle in the clouds. But real physics says such giants would be crushed by their own weight.

The key insight goes back to a 1638 book by Galileo.

1. Bone strength cannot keep up with weight gain

Take a wooden beam and scale it up 10 times in length, width, and height. Its load-bearing ability depends on cross-sectional area, which grows 100 times larger. But its own weight depends on volume, which grows 1000 times.

The result: the scaled-up beam is 100 times stronger but must hold 1000 times the weight of the original. It cannot support itself, let alone add a heavy load.

Giant bones are such beams. Scale up a human body 10 times and the bones grow only 100 times stronger, but the weight grows 1000 times. The bones snap and the giant collapses.

2. Why elephants have such thick legs

This same law explains animal body shapes. Elephants have much thicker legs than dogs, not for style but because larger bodies need proportionally thicker bones to carry the extra weight.

Small insects, by contrast, have skinny limbs because they weigh so little, and can even stick to walls using static electricity. Scale them up and they would fall off.

3. Miniature humans would struggle too

Lilliputians and other shrunk people face the reverse problem. Shrink a human 10 times: weight drops 1000 times, but bone strength only 100 times, so the tiny person is relatively strong – yet would stick to surfaces, find water like glue, and generally find life awkward.

In short: physics does not scale uniformly with size, and the size of the human body is a well-adapted compromise with those laws.