My cat is huge!

I've been told for a while by people that I have a big cat. He's been a little overweight for most of his adult life, but that is only a part of his size. In fact, I don't even think he is that much overweight. He is just HUGE! I looked up average cat sizes because I was curious, and this is what wikipedia says:
Height: 9-10 in
Head/body length: 18.1 in
Tail: 11.8 in

Well, knowing that didn't tell me much, so naturally I had to measure Gizmo. These are his dimensions:
Height: 12 in (maybe taller, he scrunched down because he didn't like me measuring him)
Head/body length: 24 in
Tail: 13 in

With that, you can see that my cat is nearly 6 inches longer than the average cat, 7 if you include his tail. I wonder if he's part maine coon . . .