The concept of a "multiverse" refers to the hypothetical existence of multiple universes or regions of spacetime beyond our observable universe. Different models and theories propose various types of multiverses, each with its own characteristics and dimensions. However, it's important to note that the concept of a multiverse is speculative and currently lacks empirical evidence.
In the context of the most well-known multiverse concept, called the "many-worlds interpretation" of quantum mechanics, the dimension of the multiverse is generally considered to be the same as the dimension of our observable universe. According to this interpretation, every quantum measurement or event results in the branching of the universe into multiple parallel universes, each representing a different outcome of that measurement. Therefore, the dimension of the multiverse would be the same as the dimension of our universe, which is commonly considered to be four (three spatial dimensions and one time dimension).
However, it's important to emphasize that the concept of the multiverse is still highly speculative and debated within the scientific community. There are other proposed types of multiverses, such as the inflationary multiverse or the string theory landscape, which suggest the existence of universes or dimensions beyond our own, but their precise dimensions and properties remain uncertain and highly theoretical.