My vet calculated out the calorie needs for my cats based on their age, weight & activity levels. Since I have a young, heavy kitty and an old, skinny one I'm feeding both the higher calorie needs of the younger one. The older one is too skinny, anyway. Bet you could find the information for your cat(s) on the internet somewhere though.
Was reading more on this topic earlier today, and saw a veterinarian refer to dry food as "diabetes in a bag". Sigh. Wish I'd known years ago. It just kills me that I've never had a vet tell me this information. They told me to get the cat to lose some weight, which I tried to do with "light" dry cat food. That's a little like telling a low carb eater to lose weight by only eating low carb pasta.....not gonna happen.
Miranda, yes the canned food is smellier.....I'm learning to adjust. The smell is preferable to the alternative though!