Okay, I have an humanoid giant that’s 50 feet, or 15.2 m, tall. If we were to scale an 1.7-m tall, 60-kg individual up to that size, they would have a mass of 43.2 tonnes. The proportional strength of humans allows them to be able to move, even under a gravity of up to 4.5 g. The giant would need to be 1.99 times stronger per mass than a human, so we could have feet that are 1.5 times wider and longer than a human’s, in terms of body proportions, as well as a body that tapers, so the head and hands are .9 times thinner proportionally.
That should be more than enough to allow the giant to move under Earthlike gravity. Next, there’s the problem of temperature. We want an internal temperature of about 310 K, and we need to find what the actual mass of the giant would be, with them tapering to be more structurally sound. As the volume will be 1.47 times higher than if proportions were consistent, so will the mass, putting the mass at an estimated 63.5 tonnes.
From that, we can use scaling laws to calculate that the giant will need 293 thousand kilocalories per day, which translates to 14.2 kW. As cellular respiration converts 64% of that energy into heat, that equates to 9.09 kW of heat. That’s about 114 times more energy than a resting human does. As we’re working with an truncated pyramid of the model of how size increases, that means that the surface area would be 108 times larger than an human’s.
If we assume that the skin increases in thickness linearly, then it’s 8.96 times thicker, which means that heat loss per mass will be 10.6% of that of a human’s. If we make it human—level thickness, then it’s at 95.1% per mass, so we will need extra-long fingers and toes to increase area enough to reach an thermal equilibrium. Finally, structures will need to be more complex to effectively deliver nutrients and oxygen, while eliminating waste. There will be a need for a lot more blood vessels, instead of supersizing existing ones.
An with the lungs, they need more alveoli, instead of scaling up the existing ones. About 720 times as much, with the lungs proportionally larger to make more space and to slightly reduce density. Now I ask, would this giant be able to survive on Earth? Why or why not?