How much bigger is the Boeing 747-8 ?

The 747-8 will feature a fuselage stretch of 18.3 ft (5.6 m) over the 747-400, bringing the total length to 250 ft 2½ in (76.264 m). The 747-8 will be the world’s longest passenger airliner, surpassing the Airbus A340-600 by 3.6 ft (1.1 m). With a maximum take-off weight of 975,000 lb (442,000 kg), the 747-8 is the heaviest aircraft, commercial or military, manufactured in the United States.

Update

The stretch was built as described: 18 ft 3 in (5.6 m) longer than the 747-400, reaching 250 ft 2 in (76.25 m) — from a 13 ft 4 in fuselage plug ahead of the wing and a 5 ft plug behind it. The 747-8 was indeed the longest passenger airliner in the world on entry into service.

One figure here was superseded. The 975,000 lb quoted above was the early programme design weight. The certified maximum takeoff weight ended up at 987,000 lb (447,700 kg), which remains the heaviest of any aircraft built in the United States.

Along with the 747SP — which had nearly 48 ft removed — the 747-8 is one of only two 747s whose fuselage length was ever changed.