Bluebulb Projects' The Measure of Things presents:
3,900 is about one-tenth the number of Seats in Fenway Park.
In other words, it's 0.1052 times the count of Seats in Fenway Park, and the count of Seats in Fenway Park is 9.5057 times that amount.
(2013 figures; daytime capacity) (a.k.a. The Cathedral of Boston) (Boston, Massachusetts)