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Understanding the Contiguous United States: What the “Lower 48” Really Means

When people discuss the “mainland” or the “Lower 48,” they’re typically referring to the contiguous United States. While these terms are often used interchangeably in casual conversation, there are critical geographic and official distinctions between “contiguous” and “continental” that matter for mapping, government reporting and demographics.

What Is the Contiguous United States?

The contiguous United States consists of the 48 adjoining U.S. States and the District of Columbia located in central North America. Officially referred to as the conterminous United States, this region excludes the two states that do not share a border with the rest of the group: Alaska, and Hawaii. It too excludes all offshore insular areas, including U.S. Territories such as Guam, Puerto Rico, American Samoa, the U.S. Virgin Islands, and the Northern Mariana Islands.

In colloquial terms, this area is frequently called the “Lower 48,” a phrase used particularly when contrasting the region with Alaska.

Contiguous vs. Continental: The Key Difference

The primary distinction between these two terms lies in the inclusion of Alaska. While “contiguous” means sharing a common border, “continental” refers to being part of the same continent.

• Contiguous United States: Only the 48 adjoining states and the District of Columbia.
• Continental United States: Includes the 48 adjoining states, the District of Columbia, and Alaska, as Alaska is part of the North American continent.

The U.S. Government often uses the term CONUS (a blend of continental and US) to refer to the continental United States. Both terms exclude Hawaii and all other U.S. Territories.

Geography and Scale of the Contiguous U.S.

The contiguous United States represents the vast majority of the nation’s landmass and population. According to Wikipedia, the region occupies 3,119,884.69 square miles. This total is split between land and water:

• Land Area: 2,959,064.44 square miles, which makes up 83.65% of the country’s total land area. This landmass is comparable in size to Australia.
• Water Area: 160,820.25 square miles, accounting for 62.66% of the nation’s total water area.

In terms of distance, the greatest great-circle route entirely within the contiguous U.S. Spans 2,802 miles between Florida and Washington state, while the greatest north-south line measures 1,650 miles.

Demographics and Population

The concentration of the U.S. Population is heavily skewed toward the contiguous region. Based on 2010 census data, over 306 million people reside in the contiguous United States, representing more than 99% of the total U.S. Population. This results in a population density of over 103 people per square mile across the Lower 48 states.

Quick Reference Comparison

Key Takeaways

• The contiguous United States (or Lower 48) refers only to the states that physically touch one another, plus D.C.
• The continental United States includes Alaska because it resides on the North American continent.
• Hawaii and U.S. Territories are excluded from both “contiguous” and “continental” definitions.
• The contiguous U.S. Holds over 99% of the total U.S. Population.