^

Detroit is a much larger city and metro.

Denver and St. Louis have very similar metro populations, but Denver's population is much more concentrated within city limits.

Kansas City's metro population isn't too far behind that of St. Louis and Denver, and KC has more people living within city limits that St. Louis does.

Detroit city ~ 670K, Detroit metro ~ 4.3M
Denver city ~ 700K, Denver metro ~ 2.8M
St. Louis city ~ 310K, St. Louis metro ~ 2.8M
Kansas City city ~ 480K, Kansas City metro ~ 2.2M

As always, city land areas vary dramatically:

Kansas City: 319 sq mi
Denver: 153 sq mi
Detroit: 143 sq mi
St. Louis: 62 sq mi