It's about the number of Keys on a Piano.
It's about nine-tenths the number of Wolves in Yellowstone National Park.
In other words, 91 is 0.8750 times the count of Wolves in Yellowstone National Park, and the count of Wolves in Yellowstone National Park is 1.140 times that amount.(a.k.a. Henihco'oo; a.k.a. Héetíhco'oo) (December 2014 figures; Wyoming Park area)
It's about three-fourths the number of Elements on the Periodic Table.
In other words, 91 is 0.7710 times the count of Elements on the Periodic Table, and the count of Elements on the Periodic Table is 1.30 times that amount.(a.k.a. Periodic Table of the Elements, a.k.a chemical elements) (confirmed elements as of 2016)
From element number one, hydrogen, to element one-hundred eighteen, ununoctium, there are 118 confirmed elements on the Periodic Table. Ninety-four of the elements exist in nature, and the remaining twenty-four have only been synthesized in labs (not having occurred naturally in the time since scientists have begun researching them)
It's about one-and-three-tenths times the number of Submarines in the US Navy.
It's about two-thirds the number of Union Stations in the United States.
In other words, 91 is 0.6740 times the count of Union Stations in the United States, and the count of Union Stations in the United States is 1.480 times that amount.(a.k.a. Union Terminal; a.k.a. Joint Station; a.k.a. Union Depot) (2016 figures)
Typically shared between multiple railroad companies and stations, there are about 135 "Union Stations" in the United States. Of these, the busiest station is Chicago Union Station, which handles 120,000 passengers each year.
It's about three-fifths the number of Moons in our Solar System.
In other words, 91 is 0.6230 times the count of Moons in our Solar System, and the count of Moons in our Solar System is 1.610 times that amount.(2015 figures) (confirmed moons only; dwarf planet satellites not included)
It's about one-and-seven-tenths times the number of Countries in Africa.
In other words, the count of Countries in Africa is 0.590 times 91.(2016 figures) (sovereign states recognized by the UN only)
The continent of Africa includes 54 sovereign countries recognized by the United Nations as of 2016. It is the second-most populous continent in the world, with 1.1 billion inhabitants.