I can't find what I read that said 4-feet, however:
Farmanimalreport says 6-feet:
"Weasels can climb hardware cloth, but this isn’t their most common
way into a chicken coop or other area. If they are in the mood for climbing and it is available to them, they will do so! But if not? They’ll find another workaround – usually right through one of your openings.
Weasels can climb up to six feet high, but they usually prefer going under or through an opening rather than climbing. This is good news for chicken coop owners, as weasels are not able to get into the coop easily if there is a fence around it. However, make sure all openings are closed off tight – if there is an opening at the bottom of your fence, even if it’s small enough that a weasel can’t fit through it, they will find one big enough to squeeze through."