Bluebulb Projects' The Measure of Things presents:
31,000 is about two-fifths the number of Seats in Lambeau Field.
In other words, it's 0.38397 times the count of Seats in Lambeau Field, and the count of Seats in Lambeau Field is 2.6044 times that amount.
(2014 figures) (a.k.a. City Stadium, a.k.a. New City Stadium, a.k.a. Titletown USA, a.k.a. The Frozen Tundra, a.k.a. The Shrine of Pro Football) (Green Bay, Wisconsin)