According to our current scientific understanding, the size of the observable universe is estimated to be about 93 billion light-years in diameter. This value is derived from the distance light has traveled since the Big Bang, which occurred approximately 13.8 billion years ago. It's important to note that the observable universe represents the portion of the universe from which light has had enough time to reach us since the Big Bang.
However, the question of the overall size of the entire universe, beyond what we can observe, remains an open topic of scientific investigation. The concept of the universe's size depends on its overall geometry and whether it is finite or infinite. Scientists have proposed different models, including the possibility of a flat or curved universe, but our understanding is still evolving.
As for the number of universes, there are various theories and hypotheses, but they largely fall into the realm of speculative physics. One concept that has gained attention is the multiverse theory, which suggests the existence of multiple universes beyond our own. These universes could have different physical laws, constants, or dimensions. However, the multiverse hypothesis is still a subject of debate and ongoing scientific exploration, and there is currently no conclusive evidence to confirm or refute the existence of multiple universes.