The Count of Things

Bluebulb Projects' The Measure of Things presents:

It's about the number of Submarines in the US Navy

(a.k.a. Subs) (includes all types, all classes) (2015 figures)
The United States Navy maintains a fleet of 72 active submarines. A typical submarine goes to sea with a crew of about 140.

It's about four-fifths the number of Keys on a Piano

In other words, 72 is 0.820 times the count of Keys on a Piano, and the count of Keys on a Piano is 1.20 times that amount.

(Moden layout; A₀ to C₇)

It's about one-and-three-tenths times the number of Countries in Africa

In other words, the count of Countries in Africa is 0.770 times 72.

(2016 figures) (sovereign states recognized by the UN only)
The continent of Africa includes 56 sovereign countries recognized by the United Nations as of 2020. It is the second-most populous continent in the world, with 1.3 billion inhabitants.List_of_sovereign_states_and_dependent_territories_in_Africa

It's about seven-tenths the number of Wolves in Yellowstone National Park

In other words, 72 is 0.6920 times the count of Wolves in Yellowstone National Park, and the count of Wolves in Yellowstone National Park is 1.450 times that amount.

(a.k.a. Henihco'oo; a.k.a. Héetíhco'oo) (December 2014 figures; Wyoming Park area)
As of the 2014 population count, there were 104 wolves living in Yellowstone National Park, in twelve packs. All of the wolves now living in the Park are thought to have descended from the 66 wolves (re)introduced into the Park in 1995-96.

It's about one-and-a-half times the number of Teeth in a Great White Shark's Mouth

In other words, the count of Teeth in a Great White Shark's Mouth is 0.670 times 72.

(Carcharodon carcharias) (average; including developing rows)

It's about three-fifths the number of Elements on the Periodic Table

In other words, 72 is 0.610 times the count of Elements on the Periodic Table, and the count of Elements on the Periodic Table is 1.640 times that amount.

(a.k.a. Periodic Table of the Elements, a.k.a chemical elements) (confirmed elements as of 2016)

It's about half the number of Union Stations in the United States

In other words, 72 is 0.5330 times the count of Union Stations in the United States, and the count of Union Stations in the United States is 1.880 times that amount.

(a.k.a. Union Terminal; a.k.a. Joint Station; a.k.a. Union Depot) (2016 figures)