You can jump to a separate table for each region of the state: Olympic Peninsula & West Coast, San Juan Islands & Puget Sound, Cascade Mountains and Eastern Washington.
1 Taylor Swift held (until this weekend) the fastest selling concert performance at Madison Square Garden for a record of 60 seconds in 2009 (source)  The Who sold out four performances at the venue in 1978 in a matter of hours per one radio broadcast announcement (source)
check the venue they are playing at and they will have a capcity if the show is sold out, it will be at capcity. It really depends on the venue. There is no average. It depends entirely on the band and on the size of the concert hall. Some artists can book themselves into Madison Square Garden in New York and draw a crowd of 15,000 people. Billy Joel played 12 consecutive sold-out performances at the Garden in 2006! Some bands play smaller halls and sell 2,000 or 3,000 or 5,000 tickets, whatever. There is no average.