According to this Wikipedia article: https://en.wikipedia.org/wiki/Shape_of_the_universe
Results of the Planck mission released in 2015 show the cosmological curvature parameter, ΩK, to be 0.000±0.005, consistent with a flat universe.
If we assume the curvature of the universe is in fact at the upper bound of this measurement (ΩK = 0.005) then what would the diameter of the universe be?
More precisely, if we assume the universe is a closed 3-sphere with ΩK=0.005, then how far would a light beam travel before returning to its source?
For reference, this article implies that the universe should be at least 14 trillion light years in diameter based on curvature estimates from the earlier WMAP mission: https://scienceblogs.com/startswithabang/2012/07/18/how-big-is-the-entire-universe
If the Universe does curve back and close on itself, its radius of curvature is at least 150 times as large as the part that's observable to us! Meaning that -- even without speculative physics like cosmic inflation -- we know that the entire Universe extends for at least 14 trillion light years in diameter, including the part that's unobservable to us today.