NOAA’s official value for the total length of the U.S. shoreline is 95,471 miles.

“The NOAA shoreline length calculation of 95,471 miles was determined by hand in 1939-40 with a recording instrument on the largest-scale charts and maps available at that time. Shorelines of outer coast, offshore islands, sounds, bays, rivers, and creeks were included to the head of the tidewater or to a point where tidal waters narrow to a width of 100 feet. For the Great Lakes, the shoreline lengths were measured in 1970 by the International Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data.”