Is there some universal limitation on the size that an extraterrestrial being could be? Or is it limitless?

Answer 1

It has to do with food available. The more food, the bigger the animal. That is why dinosaurs and even dragonflies were huge!

Answer 2

Start by examining why Earth animals are limited in size and then extrapolate. Science Fiction books can project a world with high Oxygen and low gravity which would allow larger "Intellegent" creatures.

Answer 3

I don't know the math, but there would have to be limitations on mass, because beyond a certain mass, the gravitational pull of the mass would cause it to collapse on itself, creating a black hole. So somewhere between planet size and sun size would be the upper limit on size. (My understanding is that a sun is kept from collapsing upon itself by the continuous nuclear reaction, and once the sun cools, the sun collapses). You'll have to do your own research on that one.

Answer 4

All life comes to its most productive size in a suitable environment. I imagine there would be some limits but I can't see or think of what they'd be.

Answer 5

Of different planets there may be different limits..
There are limits or earth based on gravity...