1.7 sq ft of free ventilation from those, plus your oeneings at either end....as well as openings along the entire length of the coop where the metal roof meets the walls. These aren't large openings, each being about 2"x8", but there are 16 of them.
As an aside, it's pouring rain and 39* and as I look out back at the chickens, they're all pecking around under their coop. They truly can handle the cold much better than we can!
...and somewhere along the way, my blood got thin. Its 60 here, 98% humid (maybe higher), with winds at 10, gusts twice that+, I had to put a long sleeve shirt on. The chickens don't seem to recognize me in it.
Keep up the great work, taking care of your flock.