How will I know if our kitten is fat?

Bandit is just a big boy I guess. Vet doesn't say anything to us about his weight. He carries a pouch around with him that sways from his underside when he runs. It doesn't feel totally like just skin but it hangs down from his tummy muscles too. Will he grow into it? Vet did make a comment a while back about his paws being really big. I don't know a ton about cats only having dogs growing up but I assume that is a good indication of having a big cat.

At 9mos old and 11lbs, that seems big to me! Do you have a big cat? How do you know if he's just big and not fat? Thanks!

What you are seeing is called "spay sway". Some cats get them and some don't. Mika does not have one but Bijou's is quite visible. I'm sure someone will correct me if I'm wrong, but I don't believe the kitty has to be fat to have one.

They say this pouch is after our precedessor, the african desert cat Felix Lybica. ie a desert animal-thing.

I myself believe it is a male thing - as this is mostly males having this pouch.
This pouch protecting belly from riped open and extra folds of skin around the neck being a protection in catfight fighting aggresively for revire...

Our two russian blue ex studs, a race known to be gracile, they in good shape but dont having any unnecessary fat, both do have these pouches - and the skinfolds on shoulders/neck. Neck-folds seen only when they lay down.