I don't recall ever seeing anything on this. In the cartoon Cybertron was roughly the size of Mars going by scale. But generally comics portray Cybertron as huge, Saturn-sized. This was the case in Marvel, and Dreamwave likewise reiterated a Saturn-sized Cybertron. What about IDW?
I'd assume a normal sized world, Mars to Earth range. IDW tends to the more realistic, and if they did big would likely have gravity issues.
Without a specified size, I think that Cybertron can be assumed to be of mass comparable with Earth. It could be larger in diameter if it had as many empty spaces inside as had classic G1 Cybertron. If IDW Cybertron had drastically more mass than Earth, then TFs on Earth would feel like in a lower gravity environment, and if it was lighter, then being on Earth would weight them down. So... Kinda Earth or Mars size and mass.
I don't think IDW has ever really given many hints as to Cybertron's size. But in plot terms, it's actually pretty frickin' TINY. Think about it. We almost never see any depictions of Cybertron that indicate that it has a surface area larger than, say... Oregon? Nobody ever seems to be too far from anywhere that they can't just drive there in a reasonable amount of time. In the Ironhide miniseries, it is implied that Ironhide went around killing off every member of The Swarm on the whole planet. I would say that's one complaint I have about Cybertron's handling in IDW... they have consistently avoided dealing with the planet, and its sheer size, and the potential for cultural and geographic diversity. For the first half of IDW's Transformers history, Cybertron was an uninhabitable polluted ghost town. For the last few years, it's been treated as a barely habitable barren, wild wasteland. The only time we see much of "true" Cybertron is in the flashback series or episodes, which usually take place in one city. Now Cybertron is effectively tiny... one city, with a few areas and landmarks in relatively close proximity. I think that "wiping the planet clean" as they did in CHAOS was a pretty terrible idea. They've effectively paved over 99% of anything interesting; other cities, ancient locations, old battlefields, etc, etc... instead we have a relatively bland "wild" landscape with most of its history swept away or buried. Boo. zmog
I appreciate everyone's responses. I just want to bump this topic one more time to see if any other answers come.
Cybertron could actually be much smaller than Earth. A mostly metal planet would be extremely dense, so could be smaller than Earth and still have comparable gravity. Although it could be larger if it had a lot of hollow space and tunnels beneath the surface, which is consistent with many portrayals.
I would go with something Venus-Mars Sized, so smaller than Earth. Cybertron obviously doesn't have typical planetary geography/geology so even with Comic Book Physics it can't be the Size of Saturn, that kind of mass would induce pressures and gravity that even large Robots would find difficult to shrug off and move in. Then there is all the subterranean shenanigans. Computers, Vector Sigma/Primus/Oracles at the core of the planet. The heat and pressure at such a location on something Earth sized would intense beyond understanding. But it's never portrayed as such so........much smaller than Earth. Probably.
