It's about seven-and-a-half times the number of Keys on a Piano.
In other words, the count of Keys on a Piano is 0.140 times 640.(Moden layout; A0 to C7)
It's about one-tenth the number of Bishops in the Catholic Church.
In other words, 640 is 0.11960 times the count of Bishops in the Catholic Church, and the count of Bishops in the Catholic Church is 8.3610 times that amount.(2015 figures; total Latin and Eastern Church figures; including Pope)
It's about nine times the number of Submarines in the US Navy.
In other words, 640 is 8.90 times the count of Submarines in the US Navy, and the count of Submarines in the US Navy is 0.110 times that amount.(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 twelve times the number of Countries in Africa.
In other words, the count of Countries in Africa is 0.083 times 640.(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.
It's about thirteen 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 0.077 times 640.(Carcharodon carcharias) (average; including developing rows)
It's about one-fifteenth the number of Blue Whales in the World.
In other words, the count of Blue Whales in the World is 13 times 640.(Balaenoptera musculus) (2002 estimates)
It's about one-fifteenth the number of Benches in Central Park.
In other words, the count of Benches in Central Park is 10 times 640.(Manhattan, New York City, New York)