The last thing you want is size but not weight, it should be the other way around.

The denser the muscle you put on, the heavier it is for its size. If you put on 2 stone but don't like amazingly bigger its because you've put on lean muscle. If you put on 2 stone and look like a body builder then its most likely water retention/fat.

Muscle out weights fat 3 times to one. 1kg or muscle is 3 times smaller than fat.

How old are you? We'll set you some real goals and go from there.