I have no idea the dimensions of this arena, but it was the smallest that I've (personally) ever barrel raced in it. I don't think the video shows it as well but there is very little room between barrel #1 and #2. My horse has short strides and he only got about 4 strides in there between the barrels.
My dream arena???
A football field size. So I can set up both the barrels (standard pattern) and poles at the same time to practice so I don't have to take one or the other down. AND
still have room to do reining on the other side of the arena.
We all can dream, can't we?