How is the size of the observable universe is calculated?
Oldest stars were there 13.8 billion (B) years ago, 13.8 B ly away, Beyond this it is arithmetic only. This space had expanded to about 46 Bly. Add yet-to-observe mirror image for 46 Bly. .Total: 92.
This is not my estimate
This comes from different source, without any tag of confirmation.
Had the question been about
A number of questions await definitive answer.
Is the universe finite? Infinite? Is it a sphere infinite? A finite sphere?
What matter matters for holding star systems in a galaxy? Is it Dark Matter? Or Dark Matter and more? In between galaxies? Clusters ? Super clusters? - and so on.