Up to 6 meters from arm tip to arm tip

Photo from Wikimedia Commons
Giant Pacific Octopus
The ocean's smartest invertebrate with three hearts and blue blood/Marine Life
The giant Pacific octopus (Enteroctopus dofleini) is the largest octopus species, with an arm span of up to 6 meters and a mass of around 50 kg. It has three hearts, blue blood (copper-based hemocyanin), nine brains (one central, one in each arm), and can squeeze through any opening larger than its beak. They can change color and texture in milliseconds, solve puzzles, open jars, and have been known to escape aquariums through plumbing.
Measurements
About 50 kg; record specimens over 70 kg
About 40 km/h in short bursts via jet propulsion
Body (mantle) about 60 cm
Largest suckers about 6.5 cm across
Only 3-5 years; tragically short for such intelligence