How high can chickens jump?

[LuciferRoo]

i’m thinking of re-vamping our chicken yard. Basic set up is an interior 4 ft fence (poultry wire) with a 6 ft solid wooden fence surround and a 2 ft walkway around the inner yard. The ladies have been regularly jumping the inner fence and exploring the space between the 2 fences. If we get rid of the inner fence, can they still be contained within 6 ft fencing? How high can chickens jump/flap when wanting to go vertical?

My first batch of chickens were clearing a 6' fence when young. In my case I lost the chicken lottery and had mostly cockerels.
I only had 3 pullets and cannot remember if they ever cleared that fence but multiple cockerels did and all were big boys not little game chickens.