http://www.tokyo-dome.co.jp/e/dome/architectural.htm
It doesnt include the ground level seating....I don't remember where I found Ayu's figure tough, I think it was posted back when DOME TOUR was held :x.
Does anyone remember ayu's exact stadium finale?
If its Tokyo-Yokohoma, the seating capacity is 70,000 for baseball games (not including ground level)
if it was the Toyota (I think thats what it was...but the concert footage was from many places so that could have been a different concert) then it is 45,000, not including ground level.