There is a few logical conclusion one can obtain from the Buddhist sutras. One of them is that there is infinite amount of sentient beings in Buddhism.
Here is how we can arrive at this conclusion.
Firstly, Buddhism claims that there is no beginning.
Second is that fully enlightened buddhas appears, back into the infinite past and future.
This leads to the conclusion that there was infinite number of buddhas in the past. Each time a Buddha appeared, at least one being is liberated from samsara.
Given that there is a constant reduction of total sentient beings over an infinite period until now, and the fact that there is still sentient beings in samsara. We conclude that the only way for this to happen is that there is infinite amount of sentient beings.
Assumption inherent is that no new sentient beings are "created" out of nothing. Another assumption is that there was no primordial or first Buddha.
From this, it is reasonable to further conclude that Buddhism requires infinite number of universes. Or an infinite sized universe. This is to house the infinite amount of sentient beings. This also lends credit to the teachings of pure land as a universe with that exact property.
There seems to be a disappointment to Mahayana Buddhists. If there is infinite amount of sentient beings, how can we liberate them all?
One answer I got from a zen master is: can a superhero stop all crime? Or is it enough to stop as much as they can?
The Buddha also gave this answer in a sutta. His goal is to just teach suffering and the way to end it. Who so ever follows the way, will end it, who doesn't will not.
