How much should I feed my cat

Were assist feeding him as he really only takes a few crunchy treats and licks off gravy from canned. I'm trying to figure out howmuch to feed him the vet had us on clinicare 270ml worth or 270 calories. Trying to figure out how much that would be in liquified pate cat food. For reference I am useing FF kitten turky flavored food to feed him.

well I will go look but I would guess that a regular 3 oz can is about 100 calories...