Antonov An-225 Mriya of Ukraine takes the crown of being the heaviest plane on Earth (285,000kg). Today, it is primarily deployed for commercial cargo transport.
Airbus A380-800 is a slight lighter at 277,000kg but no less a flying behemoth. It is the world's largest passenger airline. period. Airbus A380-800's usable floor space is 550 sq meters (5,920 sq ft), a staggering 40% more than the next largest airliner, the Boeing 747-8.
Stratolaunch. Third heaviest plane is Stratolaunch, a special plane (or a pair of planes) built to deliver payloads, such as satellites, into spatial orbits. It weights 226,796 kg without payload and has the longest wingspan of any aircraft at 117m.