I really would start out using approximately what the bag says - bc some kibbles are more nutrient dense than others (so the volume you'd feed is different). For example, Nature's Variety Instinct is grain free and quite nutrient dense, so you'd likely feed much less volume than a Royal Canin food. Once they've been on any food for awhile, you could feed "to condition" - meaning, feel their ribs - they should feel not to prominent and too "padded".
