I went ahead and looked up the specs myself directly on the tractor supply website. The coop states it is 4.4 sq ft to be exact. NOT 20:
I stand by everything I wrote above.
It's a waste of money. The OP good do so much better by converting a used shed.
Not sure where you read that 3 standard size birds could be housed in 4 sq ft but the standard "rule of thumb" is that they have 4 sq ft PER BIRD.
Going with the bare minimum of square footage in the run is not a good idea.
That thing is tiny. It's appalling that the literature states it can...