210 kg463 lb
Onix weighs 210 kg (463 lb), according to its official Pokédex entry, and is listed at 8.8 m (28 ft 10 in). That is very light for a snake made of boulders: by our rough estimate, a real chain of granite rocks that long would weigh around 8 tonnes. Steelix, its evolution, weighs 400 kg.
| Largest OnixPokémon Legends: Arceus, 10.56 m | 302 kg667 lb |
|---|---|
| Alpha OnixPokémon Legends: Arceus, 9.68 m | 277 kg611 lb |
| Onixofficial Pokédex weight | 210 kg463 lb |
| Smallest OnixPokémon Legends: Arceus, 7.04 m | 134 kg296 lb |
The figure is the Pokédex weight the games give for Onix: 210.0 kg, or 463.0 lb, at a height of 8.8 m (28 ft 10 in). It has not changed since Red and Blue, and Sword and Shield list exactly the same numbers.
Pokémon Legends: Arceus is the one game where individual Onix vary in size. A small one there is 7.04 m and 134.4 kg, a large one 10.56 m and 302.4 kg. Serebii lists the Alpha Onix at 9.68 m and 277.2 kg, so the biggest ordinary ones outweigh it.
The anime has its own famous Onix: Brock’s, and the Crystal Onix of Sunburst Island in episode 87, an Onix made of crystal. The show never gives either of them a weight.
The Legends: Arceus entry describes Onix as a “chain of immense stones” shaped like a giant serpent. Real rock is heavy: granite weighs about 2,700 kg per cubic metre, so a single granite boulder 1 m across weighs about 1.4 tonnes. All of Onix’s 210 kg would make one granite ball only about 53 cm across.
As a rough estimate of our own, picture its 8.8 m body as 11 boulders averaging 0.8 m across. Each one holds about 0.27 m³ of rock, so the chain holds about 3 m³. In granite that comes to about 8 tonnes, roughly 38 times the official weight. Spread over the same volume, 210 kg gives about 71 kg per cubic metre, around a fourteenth of the density of water.
None of its Pokédex entries explains this. They say the opposite, if anything: Onix feeds on boulders as it burrows, and its body hardens with age until it is like black diamond. Gyarados (6.5 m, 235 kg) and Wailord (14.5 m, 398 kg) are just as light for their size.
Onix evolves into Steelix when it is traded while holding a Metal Coat. Steelix is only a little taller, at 9.2 m, but weighs 400 kg (881.8 lb), almost twice as much. Its Pokédex says an Onix that lives over 100 years becomes diamond-like in composition, which at least fits the extra weight.
Mega Steelix grows to 10.5 m and 740 kg (1,631.4 lb), more than three and a half times the weight of Onix. In Legends: Arceus, Steelix ranges from 256 kg for a small one to 576 kg for a large one.
Low Kick and Grass Knot get stronger the heavier the target is, and reach their maximum power of 120 against anything over 200 kg. Onix clears that line by just 10 kg, so it always takes the full-power version. That hurts: Grass Knot is four times as effective against its Rock and Ground typing, and Low Kick twice.
Onix can learn Heavy Slam, from TR79 in Sword and Shield or as an egg move in X and Y. With its 210 kg, the move has 120 power against targets under 42 kg, 100 up to 52.5 kg, 80 up to 70 kg, 60 up to 105 kg, and 40 against anything heavier.
Onix weighs 463 lb, which is 210 kg. Its evolution Steelix weighs 881.8 lb (400 kg).
The Pokédex lists Onix at 8.8 m, or 28 ft 10 in, which makes it the tallest of the original 151 Pokémon. Since it is a long serpent, that figure is closer to its length than to how high its head reaches.
The games never say. Its entries describe a body of hard stone that eats boulders, yet a real chain of rocks its size would weigh several tonnes, not 210 kg.
No. Gyarados weighs 235 kg, 25 kg more than Onix, even though Onix is listed 2.3 m taller. Both are far lighter than Snorlax at 460 kg.
No weight is given. The Crystal Onix only appears in the anime, in the Orange Islands episode “The Crystal Onix”, and the show never states its size or weight.
Last checked October 3, 2026.
