Bluebulb Projects' The Measure of Things presents:
13,000 is about one-third the number of Seats in Fenway Park.
In other words, it's 0.350680 times the count of Seats in Fenway Park, and the count of Seats in Fenway Park is 2.85160 times that amount.
(2013 figures; daytime capacity) (a.k.a. The Cathedral of Boston) (Boston, Massachusetts)