14-1/4" Wide x 11-1/4" High x 5-1/2" Deep. The 1100C-E box when expanded is the same size as the standard 1100C. We have made it this way to conserve storage. This enclosure is installed between 16" centered studs prior to the application of final exterior siding material. The enclosure has an open top and bottom to the inside wall and a 1/2" plywood backboard for mounting utility equipment. The fully enclosed lid seals off outside weather and insects and is fastened with two zinc-coated phillips sheet metal screws.