Catster reports that a healthy, active 8-lb. adult cat should consume about 30 calories per pound per day, or about 240 calories per day. On average, dry food contains about 300 calories per cup, and canned food has about 125 calories per 3 ounces. So, an 8-lb. cat needs about 4/5 cup dry food or just under 6 ounces of canned food per day. These are only averages, as cats can vary greatly in their nutritional needs. Consider her activity level, and consult your vet to help determine her healthy weight.