Okay, lets do it this way.
What I'm saying is that on here I've seen people say you need 10 square feet per bird in a run? This is wrong then?
In my humble opinion, yes. Much of what you get here is purely anecdotal, and there are widely divergent opinions.
I have four birds, if we only end up keeping two or three then my backyard (which is 33' X 64') should be more than big enough for them
You will be fine, considering your now disclosed dimensions (33' X 64') for the yard, their "run." That is a wholly adequate space.
I don't understand what you're saying in relation to the 87 feet thing...meaning, you have a run that has 87 square feet per bird or their general living area (backyard) should be this large?
Yes, and Yes. They live in what is a range of 87 sq ft per bird. That it is fenced, makes it a "run." Their house is only one feature within this range/run.
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Now for the back story.
All rearing is confined, unless you have no structures or limits and allow your birds to literally run amok. Any other treatment is confining them to some degree.
What I'm implying by my comments is that there are no absolutes here... all confinement leads to consequences. The closer you confine them the worse these become.
I personally detest that set of consequences and now see the back of such methods for all the reasons mentioned. I rely on the old, "500 birds per acre" formula from a century ago - thats 87.12 sq ft per bird. It happens to be the space our range-rearing grandfathers worked out as adequate for the land itself to manage the waste from chickens.
I haven't dealt with muck, manure or disease since I started using it.
You asked for a number, I gave that. My sincere apologies if I presented it wrongly. It wasn't manufactured by me - it was proven before we were born. That so many choose to ignore it is regrettable.
I appreciate your comments; so thank you. I see that you are literal minded and some sort of defined formula indeed suits you best.
But let me offer you this warning: While opinions differ, there are some hard and fast rules one should not tempt. Much of what is accepted as good practice stems from error and outright lore. Without knowing it, well-meaning people adopt relatively intensive management practices, thinking they're good to go. Only later do they realize something is up... and it aint good.
Again, you should do well in your space. Sorry if I muddled the discussion.