I used 1" x 2" 14 gauge welded wire. That was after a running battle with a skunk that kept digging it's way into my horse barn to steal cat food. It managed to slip through a 2" crack.......so I decided 2" x 4" wire was too large.
If you have weasels, even 1" x 2" may be too large. Especially so for that skinny little least weasel if you have to deal with one of those.