Ribs may be visible in short coated cats. Bones can be easily felt with minimal or no fat cover. Abdominal tuck after the rib cage is very pronounced. In very thin cats loss of muscle mass may be visible.
Ribs should be easily felt, slight fat covering and a waist (abdominal tuck after the rib cage) should be viewed from side and above.
Cats are classed overweight if they weigh 10-20% more than their ideal body weight. Ribs cannot be easily felt. The waist is starting to disappear and the back looks broader. The abdomen is starting to become rounder and may begin to sag.