How small does a travel mirror need to be to fit in a carry-on or purse?

Pocket compacts (around 3-4 inches folded) disappear into a handbag but only show one feature at a time. Folding tabletop models in the 5-inch class fold roughly to the size of a small tablet and were the most-recommended format in r/HerOneBag and r/onebag threads for one-bag travelers who still want a usable face-sized view.