It's looking like it will be a decent attendance - loads of areas on the online seat finder are red and amber, and I could only find 2 seats together in the whole Main Stand.
I reckon it will abround 25,000.
Although, I also though the Sheff Weds match would be sold out (because of the Derby priority) ... but only about 24,000 showed up for that, including 4,000 Wendies.