1 kilometre!
The Boeing Everett Factory is an aircraft factory in Everett, Washington, in the United States, built in 1967 to make the Boeing 747 jumbo jet. Its main assembly building is the largest building in the world by volume as of 2026. It encloses about 13.4 million cubic meters (472 million cubic feet) of space and covers 39.8 hectares (98.3 acres). Boeing describes the building by its volume and floor area rather than its length, so the 1 kilometer (0.6 miles) shown above is not an official measurement.
Boeing, Guinness World Records and NASA all describe this building by the space it encloses and the area of its floor. Guinness lists it as the largest building in the world by volume. Its floor covers 39.8 hectares, and the whole Everett site, with its paint hangars, flight line and other buildings, covers about 414 hectares (1,025 acres).
An area is not a length, but it can be pictured as one. A square with the same area as the building's floor would be about 630 meters (2,070 feet) on each side. The building has six assembly bay doors, each 25 meters (82 feet) high and 91–107 meters (300–350 feet) wide.
In the mid-1960s Boeing set out to build the 747, a jetliner meant to carry more than 350 passengers. It would be about two and a half times the passenger capacity of the largest airliners of the day. The company needed a new factory to match. The first production workers arrived at Everett in January 1967, and the main assembly buildings opened on May 1, 1967.
Workers assembled the first 747 while construction crews were still building the factory around them. The factory was completed in 1968, when it enclosed about 5.6 million cubic meters. It has since grown to about 2.4 times that volume.
Boeing added about 20 acres (8 hectares) of factory for the 767 in the late 1970s and planned another 36 acres (15 hectares) for the 777 in the early 1990s. The 747, 767, 777 and 787 have all been assembled there.