Why Giants Can’t Exist: The Physics of Scaling and Bone Strength

Why are there no giants? Because size matters for organisms. If we take a human such as Dwayne Johnson as a standard sample and double his height, his overall weight would increase eightfold as height, width, and thickness increase.

At first glance this may not seem problematic, but if the giant were to walk upright, his leg bones would have to bear eight times the weight; do they have that strength?

Obviously not. In the process of doubling height and increasing volume eightfold, bone strength undergoes two effective doublings (changing shape and thickness) and one ineffective doubling (lengthening). For a column, lengthening does not increase strength, so lengthening leg bones does not improve their load‑bearing capacity. The added length not only fails to raise strength but also forces the base to support more weight.

Now Dwayne Johnson’s leg bones can no longer meet the weight demands: bone strength is only four times the original, while body weight is eight times, creating a mismatch. If his height keeps increasing, his leg bones will soon reach their limit and break under the torso’s load.

This process is called isometric (equal) scaling, where length, width, and height are scaled proportionally. It is not a viable method for creating large organisms; instead, allometric scaling—adjusting internal proportions as size grows—is required.

When an animal’s height grows, its legs must become thicker to support the added pressure. This explains why cats survive with slender limbs, while elephants have pillar‑like legs.

This rule applies not only to Dwayne Johnson but to all of us, which is why giants can only exist in myth.

[US] Ben Orlin, translated by Tang Yanchi, "Math Changes: A Joyful Math Introduction Full of Silly Illustrations"