Astronomers don't estimate the *size* of the universe, but rather its observable size. This is because we can only see as far as light has had time to reach us since the Big Bang.

Here's what we know:

* The observable universe is about 93 billion light-years across. This means that the most distant objects we can see are 93 billion light-years away.

* The universe is expanding. This means the distance between galaxies is constantly growing, so the observable universe is getting bigger all the time.

* We don't know how big the whole universe is. It could be infinite, or it could be much larger than the observable universe.

Key point: The observable universe is just the part we can see, and the true size of the universe remains a mystery.