What is the biggest rocket ever built?

Since its first integrated flight on April 20, 2023, from Boca Chica, Texas, SpaceX's Starship and Super Heavy stack is the tallest, heaviest, and most powerful rocket ever to have launched. With the ship mounted, it stands about 120 m tall, has a 9 m diameter, and its mass on the pad is around 5,000 t, almost all liquid methane and oxygen. The booster's 33 Raptor engines generate more than 70 MN of thrust, nearly double the Saturn V. Both elements are designed to be fully reusable: in October 2024 the launch tower caught a Super Heavy in flight with its arms for the first time.

NASA's Saturn V was the benchmark for more than half a century: 110.6 m tall, 10.1 m in diameter, 2,900 t in mass, and 34.5 MN of thrust from its five F-1 engines. It flew thirteen times between 1967 and 1973 without losing a single payload and carried the Apollo program's astronauts to the Moon. The Soviet Union built the N1, 105 m tall with 30 engines on its first stage, for its own lunar program; its four launches between 1969 and 1972 all failed. The Soviet Energia (1987) and NASA's Space Launch System (2022) matched or slightly exceeded its thrust, but not its height or payload capacity.

Height, mass, thrust, and payload capacity don't always line up. The Saturn V, with about 140 t to low Earth orbit, was for decades the leader in demonstrated capacity; Starship is designed to comfortably surpass it, though the real figure depends on the version and on whether the vehicle is recovered or not. In diameter, the Saturn V and the N1 both exceed Starship. So depending on the criterion, the answer changes; in physical size and thrust, there's no doubt: Starship.