We have a blenhiem cavy who is 16months old and weighs 9.5 kgs. When will he become fully grown and what should his ideal weight be

The breed standard says 12-18 lbs so im guessing he should be somewhere around that range. I wouldnt worry if he is slightly more or less aslong as he isnt obviously over or under weight.

It also depends on how big a frame your dog has A cavalier between 11lbs & 18lbs look quite small(I know I have one who weighs 15 lbs)& so as long as he isn't fat & you can feel his ribs & he has a waist he could be upto 25lbs & still not be fat ;) if my little one weighed 18 lbs he would look gross

my 11 month old cav weighs 13kg and he is not fat he is just a big dog and i really hope he has stopped growing.

How tall is he? Just curious as that really is one large Cavalier. :)

My almost 11 year old Blenheim weighs 9.1 kg and he's just right -he's quite averaged sized as well. The smallest I've had was a ruby bitch who weighed in at 6.5.kgs.

I have two cavs, one is nearly 4, his height is 13 inchs and he weighs 10kg but you can see his waist and then my other one who is 3, is quite big for a cavalier (we call him a gentle giant!).  His height is 15 inches and weighs 13kg but again you can see his waist and feel his ribs.

My 14 month girl weighs 10kg, she's a bit up to size but not fat. My 3 1/2 year old boy weighs 10.5 kg, he's about average size though somehow gives an impression of being bigger than he is. People at shows are always surprised when they pick him up as he doesn't look like he weighs that much. Good thing there aren't many weight classes for Cavaliers!! :-)

My two girls both weigh 7kg and are perfect even though one looks smaller thaan the other. I guess there just like us in that respect. :)

My 11 month old Blenheim weighs 10.2kg, which is more than she should (according to breed standard), but she is also 2 inches taller than breed standard.  You can see her waist and feel her ribs when you stroke her.  Before she was spayed she was 9.6kg and people would stop me in the street and say she looked "slim" but you could tell they wanted to say "thin".  But she eats well, isn't a pig, she'll eat what she wants/needs and leave the rest.  She's never been greedy and we don't feed her loads of biscuits or titbits.  She has regular check ups at the vets and the vet has never said that she's overweight.  I've seen plenty of Cavaliers who look like their skin is about to burst because the owners can't resist their puppy dog eyes.

As long as you an see his waist and feel his ribs (not see them), he should be fine.  I'd say he's probably fuller grown now. 

but she is also 2 inches taller than breed standard

Er there is no height given in the breed standard

Size
Weight: 5.4-8.2 kgs (12-18 lbs). A small, well balanced dog well within these weights desirable

My youngest is now spot on the 18 lbs(been on a bit of diet) & JD is 15lb of pure muscle literally he looks like a puppy along the "big"boys & has something few cavaliers have a well developed second thigh LOL one judge tiold me there was something wrong with his back legs LOLOLOLOL Yep there is it called muscles !