This Mega Monster Cat May Become the Biggest Cat In the WorldJesus Diaz6/11/12 1:29am1811EditPromoteGo to permalinkMaine Coon is a breed of domestic cat. They're usually pretty big. The biggest specimens weigh up to 25 pounds—11.3kg. But Rupert here isn't just pretty big. He's huge. He's a "mega monster cat," according to the experts.