The CIA World Factbook lists the land boundaries of the United States as 12,248 kilometers (7612 miles), and the coastline as 19,924 km (12,383 miles). These numbers include all US territory.
With over 12,000 miles of coastline I doubt anyone has counted. I suppose technically, since a beach is where the water meets the shore, there are two for the continental US, one on the west coast and one on the east coast.
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