The size of the universe is not determined by the number of particles it contains. Instead, the size of the universe refers to the spatial extent of the observable universe, which is the region of the universe that we can potentially observe given the current age of the universe and the finite speed of light.
The observable universe is estimated to have a diameter of about 93 billion light-years. This is because the universe has been expanding since the Big Bang, and light from the most distant regions of the universe has had enough time to reach us.
However, if we consider the entire universe, including regions that are currently beyond our observational reach, it is uncertain what its true size is. The universe may be much larger than the observable universe, possibly even infinite in size, or it may have a finite but unknown size.
It's also important to note that the term "particles" typically refers to subatomic particles like protons, neutrons, and electrons. The universe is not made up of discrete particles in the sense of being confined to a single location. Instead, it consists of vast cosmic structures like galaxies, galaxy clusters, and superclusters, as well as dark matter and dark energy. These components are distributed throughout the vast expanse of the universe.