According to the United States Census Bureau, the city has a total area of 143.0 square miles (370 km2); of this, 138.8 square miles (359 km2) is land and 4.2 square miles (11 km2) is water. Detroit is the principal city of the Metro Detroit and Southeast Michigan regions.

The highest elevation in the city is in the University District neighborhood in northwestern Detroit, west of Palmer Park, sitting at a height of 670 feet (200 m). Detroit's lowest elevation is along its riverfront, sitting at a height of 579 feet (176 m). Detroit completely encircles the cities of Hamtramck and Highland Park. On its northeast border are the communities of Grosse Pointe.The Detroit River International Wildlife Refuge is the only international wildlife preserve in North America, uniquely located in the heart of a major metropolitan area. The Refuge includes islands, coastal wetlands, marshes, shoals, and waterfront lands along 48 miles (77 km) of the Detroit River and Western Lake Erie shoreline.

Three road systems cross the city: the original French template, radial avenues from a Washington, D.C.-inspired system, and true north–south roads from the Northwest Ordinance township system. The city is north of Windsor, Ontario. Detroit is the only major city along the U.S.-Canadian border in which one travels south in order to cross into Canada.

Detroit has four border crossings: the Ambassador Bridge and the Detroit-Windsor Tunnel provide motor vehicle thoroughfares, with the Michigan Central Railway Tunnel providing railroad access to and from Canada. The fourth border crossing is the Detroit-Windsor Truck Ferry, located near the Windsor Salt Mine and Zug Island. Near Zug Island, the southwest part of the city sits atop a 1,500-acre (610 ha) salt mine that is 1,100 feet (340 m) below the surface. The Detroit Salt Company mine has over 100 miles (160 km) of roads within.