Royal Canin SO wet for cats...How much to feed him?

My cat was prescribed Royal Canine SO.  
He is 6 years old, and around 16 lbs at a healthy weight.

He is now on only this food and I am wondering how much to feed him.

According to the Royal Canine site, they say over 2 cans which seems like a lot...and I've been told by vets that these numbers are usually high.

What is the proper amount?

[Aleda M Cheng, D.V.M., C.V.A]

The average sized cat is supposedly 9 pounds and the optimal amount for this size is half of one 5.5 ounce tuna sized can of cat food twice daily.

Your cat is almost double that weight.  I would try feeding the two cans and monitor his weight very carefully.  He may not even eat the full two cans.  Please weigh him weekly and record his weight.  There will be minor fluctuations for a couple of weeks.  If after one month his weight has averaged out to still be 16 pounds than the two cans are the correct amount to feed.  However, if he has gained weight,  than feed a bit less; it he has lost weight feed a bit more.  

Cats can have cyclical weight fluctuations also.  They tend to gain a bit in the winter and lose the excess in the spring and summer.  Take all of this into consideration.