According to the United States Census Bureau, the CDP has a total area of 5.7 square miles (14.8 km²), of which, 5.2 square miles (13.5 km²) of it is land and 0.5 square miles (1.3 km²) of it (8.76%) is water.
The cut through South Padre Island has shoaled considerably and as of early 2008, only shallow draft boats could safely enter at the Mansfield cut.