Or to put this astonishing thing into perspective;
Stratolaunch
wingspan of 117 m (385 ft)
MTOW 1,200,000lb (540,000Kg)
Payload 500,000 (227,300Kg)
B747-400
Wingspan 211 ft 5 in (64.44 m)
MTOW 875,000 lb / 396,890 kg
APS 404,600lb / 183,520kg
C17
Wingspan: 169.8 ft (51.75 m)
Empty weight: 282,500 lb (128,100 kg)
Max. takeoff weight: 585,000 lb (265,350 kg)
An225
Wingspan: 88.4 m (290 ft 0 in)
Empty weight: 285,000 kg (628,317 lb)
Max takeoff weight: 640,000 kg (1,410,958 lb)
(figures from Wikipedia)