What kind of chickens are they? Banties fly better than large birds. They'd need a top of some sort or you;d have to clip their wings. Large birds, like Reds or Rocks can fly a little, but four or five feet should keep them in. For a few extra dollars I'd use 6ft welded wire as added insurance.
Hi, Welcome !!!
My fence is four feet high. I bought a roll of chicken wire and post. I have a post about every 6 feet. You may want to steak down the bottom with plastic or metal tent steaks to keep predators from slipping under and eating your bird's.
I have had all sorts of wild beast digging under the wire to gain access to the inside.
They lucked out and killed three of my Duck's.
Dug a whole and bent the wire and had a 'Duck Buffet" for dinner.
That was Before I steaked down the wire. Also, the chickens will slip out from underneath if they are really determined to free range.
Is this your first Chicken family ?
What kind of dog? Some dogs will care less about getting your birds, some live for it. I have German Shorthaired Pointers and they make a living hunting birds.
I have 6ft welded wire fence with the bottoms bent and stuck 4 inches under the soil. Around the bottom I have 24 inches of chicken wire to keep the younger bird's heads inside the fence. That set up keeps my dogs out and the birds in.