How big do Siberian get?

All about the Neva Masquerade
Siberians are heavy cats – when fully mature, you should expect 6-7kg for males; females will be around 4-6kg. They’re not supposed to be oversized or cartoonishly large like a Maine Coon, though – if Maine Coons are the Great Danes of the cat world, Siberians are the Bullmastiffs.
Siberians are heavier than they look, with big solid bone, round heads and bellies, and a lot of muscle. They grow slowly and mature over a full four or five years. Males typically put on about a half a kg a month until they are a year old, and then add their last 2kg over the next few years. Females at their first birthday are usually under 5kg, and still very much kittens. By the age of three they have their full size, but continue to bulk up until age five.