how thick should concrete slab
Recommended thickness of concrete slabs. 1  Driveways: 6 - 8 inches (0.15 - 0.2 m). 2  Side walks, barn and granny floors: 5 - 6 inches (0.125 - 0.15 m). 3  Porches, Home garage floors: 4 - 5 inches (0.1 - 0.125 m).