Hi, Rosie here. I have a question for y'all. So I'm building my coop at the moment, and I had this idea to put in a pet door to let the chickens get from the garden shed outside to the run. I'd remove the flap or rig it to stay up, of course, but it makes me feel like the girls would be a bit more secure, in case something manages to get into the run. Here's the deal, though. New Egg as I am, I don't actually know how big a full grown hen is! Silly me! Ok, well, would a chicken fit through a cat door? It's 6 and a quarter by 6 and a quarter-- 15.88cmx15.88cm.