??? I think must be a general rule, but that it really depends upon the cat. Cassy is roughly 14 pounds, but very muscle-y and athletic. We (vets included) were worried last year when he lost a pound. (He had eating problems after his litter mate Sassy died and before Livvy came to live with us.)

My vet uses the ground rule about feeling ribs and his are very 'feelable'. Livvy's are somewhat less so...