Its western terminus is at SR 207, and its eastern terminus is at County Road A1A (CR A1A) near St. Augustine Beach.

About 0.4 miles (0.64 km) east of the western terminus, SR 312 passes over the Florida East Coast Railway main line via an overpass.

one mile (1.6 km) from the western terminus, SR 312 intersects U.S. Route 1 (US 1), with SR 312 continuing a few blocks east through St. Augustine until the Mickler-O'Connell Bridge over the Intracoastal Waterway.

Continuing east, the state highway ends at the point CR A1A transitions to the roadway to continue heading east.

Media related to Florida State Road 312 at Wikimedia Commons