How heavy is Gyarados?

The figure is the Pokédex weight that the games and pokemon.com give for Gyarados: 235 kg, or 518.1 lb, at a height of 6.5 m (21 ft 4 in). Scarlet and Violet list the same numbers.

Pokémon Legends: Arceus is the one game where individual Gyarados vary in size. A small one there is 5.2 m and 150.4 kg, a large one 7.8 m and 338.4 kg. Oddly, Serebii lists the Alpha Gyarados at 7.02 m and 304.56 kg, so the biggest ordinary ones outweigh it.

The famous red Gyarados of the Lake of Rage, met at level 30 in Gold, Silver, Crystal, HeartGold and SoulSilver, is a Shiny Gyarados. Only its color is different: it has the same Pokédex height and weight.

For a serpent 6.5 m long, 235 kg is very little. As a rough estimate of our own, treat its body as a tube 6.5 m long and 0.6 m thick: that is about 1.8 m³. Something that size with the density of water would weigh around 1,800 kg, so the official weight is only about an eighth of that.

Gyarados is not alone. Wailord is listed at 14.5 m, more than twice as tall, yet weighs only 398 kg. Pokédex weights are often far below what a real animal of the same size would weigh.

Magikarp is 0.9 m long and weighs 10 kg. It evolves into Gyarados at level 20 and becomes 23.5 times heavier.

Mega Gyarados keeps the same 6.5 m height but adds 70 kg, for a total of 305 kg (672.4 lb). It also changes type from Water and Flying to Water and Dark.

Low Kick and Grass Knot get stronger the heavier the target is, and reach their maximum power of 120 against anything over 200 kg. At 235 kg, Gyarados always takes the full-power version, and so does Mega Gyarados. Its small Legends: Arceus size, at 150.4 kg, would fall into the 100 power band.