Q.  How big is the Universe?

A.  The Universe does not have any size, as it is infinite in space and time.

Q.  Why does the conventional answer say it does?

A.  Usual answers are based on the Big Bang Theory, which is wrong.

Q.  Why do you say it is wrong?

A.  You can go to Correct-Answer to Question #3: Is the Big Bang Theory Correct? for this.