Switching a cat on a diet to wet food.

I grew up thinking that dry kibble was "real" food and wet food was a treat. I never questioned it until finding this site. My vet has instructed me to feed my cat 1/4 cup of dry food twice daily in order to get his weight down. He is currently 17 pounds. He is half Maine Coon, to me he doesn't really seem like he needs to lose much weight. 

I was planning on switching him to a mainly wet food diet, but I have a couple concerns. Firstly, should I still feed him 1/4 cup twice daily? Should I supplement it with any dry food? Also his poo is quite runny whenever he gets canned food, is this just because his body hasn't adjusted to wet food? I usually get him Wellness brand, any suggestions on a better quality brand? 

The easy things first! No, you wouldn't feed 1/4 cup of wet food a day and no, you don't need to supplement with dry food. It's great that you want to switch your cat to wet food: it's easier to keep a cat's weight in check on high-protein, low-carb wet food.

As for the runny poo question. It's hard to say what caused that: some cats respond more to changes in food than others. Or it could be that a certain ingredient bothered him: potato, for example, which is in some Wellness foods, bothers some cats' stomachs. Which Wellness food were you feeding? Did that food have anything in it that's not in the dry food you've been feeding?

The wet food I give him is usually Wellness Core Beef, Venison, and Lamb but I've given him the Wellness Core Indoor Formula as well. Neither of those have potato in them. I currently feed him Blue Buffalo Wilderness Indoor Chicken dry food. His dry food definitely has more ingredients. Perhaps I should try another brand of wet food and see if it has the same results? 

Also, do you know how much wet food to give? Thanks so much for your help  

I have to be very quick but wanted to say that yes, I'd definitely try another kind of wet food, introducing it very slowly... maybe starting with chicken since that's what's in his dry food so you know it's not, say, the beef or venison that bothered him in the Wellness Core.

As for amounts, I'm terrible on that, though @LTS3 is great on those questions. There's a certain number of calories per pound of weight that's considered "typical" for feeding but of course how much you ultimately feed can vary depending on your cat's activity. (Our cats are very active and eat a ton so I'm lucky not to have to count calories! I suspect they're well over the typical recommendation.)

Thanks so much for the help! I greatly appreciate it.

If this were my cat I would just switch him to 100% wet food and throw out the kibble, as long as he eats the wet food. I'm not a big fan of Wellness. If you've noticed he's had tummy issues on that brand of wet food perhaps try something else. Good ones that aren't full of bad ingredient are Tikicat, Weruva, Feline Naturals, ZIwipeak, Merrick LID. It would probably help to mix in a digestive enzyme or probiotic to his wet food, too.