The United States is made up of 50 states, but 48 states – also known as the conterminous states, the lower 48, or the contiguous states – are adjoined.
Two of the states – Alaska and Hawaii – are not part of the lower 48 states. This is because Alaska is separated by British Columbia, Canada, and Hawaii is an island. Washington, D.C., is also part of the contiguous United States, although it is not an official state. The contiguous United States is not to be confused with the continental U.S., which includes the state of Alaska.
The lower 48 states, along with D.C., have an area of over 3.1 million square miles. Water makes up over 160,000 square miles or over 62% of the world’s total water area. The remainder is land area and is similar to the size of Australia.
Based on census data from 2010, over 306 million people live in the contiguous United States. This makes up over 99% of the country’s total population. The population density of just the lower 48 states is over 103 people per square mile.