Once you have chosen a suitable food you need to decide how much to feed and how often. The top manufacturers all provide recommendations on the packaging as to how much of their product to feed and these can be used as a guideline. However cats generally are very good at regulating their own food intake and so it is acceptable to leave food available for them all day unless the cat is overweight. They will eat only what they need. A convenient way to feed a cat is to buy a purpose built automatic feeder and keep it topped up with biscuits. Provide a clean and quiet feeding area away from heavy foot traffic or competing animals.
Ideal body condition is when you can easily feel the ribs with gentle pressure but cannot see the ribs. The fat pad under the belly should be minimal.