I do not think we know for sure the size of the universe yet, because we can only probe a small part of it. Whether the universe is finite or infinite, depending on the "curvature" of the universe.

Imagine we look at a globe, whose surface is a two dimensional sphere. The global has a finite surface area, because it has a positive curvature. If we reduce the curvature of the globe, its size gets bigger and bigger. And if the curvature is zero, the globe becomes infinite, because effectively the globe becomes a flat two dimensional plane without boundaries.

The universe could be thought of as a three dimensional sphere. We can estimate the size of the universe (if it is indeed finite), by measuring its curvature. This can be done even though we cannot see the entire universe. So far the understanding is that, the curvature of the universe is nearly zero, which means that the universe may as well be infinite, or at least much bigger than what we can see.

The diameter of the observable universe, according to Google, is estimated to be 91 billion light-years (about 28x10⁹ parsecs ~ 5.4 x10²³ miles)! I hope this helps!

-We can see out into the universe a distance of about 14 billion light years. This is because the universe is only 14 billion years old, and so light has had only 14 billion years to travel. The real universe is probably much bigger than this, and may indeed be infinite. Within the 14-billion-light-year radius that we can see, there are about 50 billion galaxies, and the average galaxy contains about 100 billion stars.