What is the size of the observable universe?
As of now, the first formed stars are about 13.82 billion years old. HST-discovered-galaxy GN-z11 is a little younger but farthest. So, the tentative size of observable universe is 2 X 13.82 bly.
With further advances in the telescope-technology, for higher-than before-limits, these approximations might be revised, in due course of time.
The size 27.64 bly includes, by extrapolation, yet-to-be-detected virtual antipodal universe of size 13.82 bly.
Reference for the farthest galaxy discovered by Hubble Space Telescope: