There's not really a short answer to this, but OP of this thread goes over the size in detail Transformers has 3 known "main" multiverses (I haven't researched the Dead Multiverse at all though), however the size of them is waaaaaay bigger than your standard infinite multiverse since each universe has an "Uncountable Infinity" of branch universes, and even the smallest uncountable infinity is infinitely larger than a "countable infinity". This makes the equivalent universes of just the main Positive multiverse roughly equal to an infinite amount of multiverses per universe It is ridiculous, but that is the information we have to go off for now. There are tons of statements about all possible versions of, and hypothetical versions of, the universes existing. So we know this ridiculous amount of branch realities are real and that Primus/Unicron/The 13 perceive them even if sometimes they are short-lived or something.