Oh, friend. I feel this question in my bones, and not just because I've spent far too many evenings crouched in a coop, counting feathers like a deranged accountant. You're getting 11 Brahma chicks, which is basically adopting a flock of feathered mini-horses with attitude problems. And you're asking the age-old question that has launched a thousand forum threads: does the square footage count the run or not?
Here's the thing, and I say this with love and a healthy respect for your upcoming sleep deprivation: the numbers you've seen floating around are not a magic spell. They're a starting point. The rule of thumb you keep hearing, something like 4 square feet per bird inside the coop and 8 to 10 in the run, is a guideline for *minimum* comfort. It's not a law of physics. Your Brahmas are big birds, so they're going to need more room than a bantam, but the real issue is what happens when they're stuck inside. If you're closing them in the coop at night, that's where the sleeping, the roosting, and the inevitable "who gets the corner spot" negotiations happen. That's where the 4 square feet matters most, because nobody wants a pile of grumpy, cramped giants pecking each other at 3 AM.
But here's the practical kicker: you're also planning to let them free range most days. That changes the math entirely. When they're out in your yard, they're getting all the space they need to stretch, scratch, and engage in their favorite sport of "pretend the grass is lava." The run becomes a backup plan, a holding cell for when you're not home. So your real question isn't "what's the minimum," it's "what's the least amount of time they'll be stuck in that run without wanting to stage a mutiny?" If you're gone for 10 hours and they're cooped up, you need that run to feel like a playground, not a prison. I'd say cramming 11 Brahmas into a tiny run is a recipe for bored, destructive, and frankly, *loud* birds. They'll start eating each other's feathers out of sheer spite.
Plan for the run to be your big-ticket item. Make it roomy, make it fun, give them things to climb on and peck at. And for the coop itself, don't skimp, but don't stress over an extra half-foot per bird. A slightly cramped coop that's clean and safe is better than a palatial one that's drafty and full of mites. You're not building a chicken hotel; you're building a safe house. The free-ranging time is what will save you from the chaos. If they're out in the yard all day, they'll forgive you for a slightly snugger night spot. Just don't try to pull a fast one on them. They know. They always know. And they will absolutely judge you for it from atop the fence line while you're trying to herd them back in. Good luck. You're going to need it, and a solid pair of boots.