“according to older versions of the CIA World Factbook (from 1982 to 1996), the U.S. was listed as the world's fourth-largest country (after Russia, Canada, and China) with a total area of 9,372,610 km2. However, in the 1997 edition, the U.S. added coastal waters to its total area (increasing it to 9,629,091 km2). And then again in 2007, the U.S. added territorial water to its total area (increasing it to 9,833,517 km2). During this time, China's total area remained unchanged. In other words, no coastal or territorial water area was added to China's total area figure.”

-From the source of the rankings(Britannica, United Nations)

So basically in the US we acknowledged China was bigger until 1997 then decided to count 100 miles of water off our entire coast to boost our stats. Hawaii too and I bet we even counted Puerto Rico to boost our stats even though we won’t allow territories to become actual states and get the benefits. Which isn’t a big deal but it is a lil lets wave our dick in the wind uncle sam type of thing.