If something is so big you can’t even guess at its size, you’d call it inestimable. It can describe physical size (the inestimable universe) or a degree of something (your inestimable handsomeness with that new haircut).
The prefix in- means “not,” and estimable has the same root as the word estimate, which means "to take an educated guess." Sometimes a thing is so great that you cannot even guess. A tsunami causes inestimable destruction. You’d need to travel inestimable miles to reach the edge of the universe. The love you have for your pet raccoon is inestimable, but the number of times she gets into your trash every week is quite estimable.