When is it okay to move up a violin size? I have a 3/4, I've had it for about a year now, and it's a bit small. But when I try the 4/4, it's a little bit big. How can I fully determine if it is actually to change?
The rule of thumb for fitting a violin is to put it on your shoulder as though you were going to play, and put your hand around the scroll. If you can cup the scroll without strain on a 4/4, you can move up in size. Some people actually prefer the smaller instrument even though they could use a 4/4 by this test, so if the full size really feels to big even after an extended time trying it, think about using the smaller instrument.
The new instrument will take some getting used to, and will feel too big at first. It will take a few hours at least to get used to it. If you play daily, you should adapt within a week or two.
If you have a teacher they can help you decide what size you should use, and when it is time to move up. If you can go to a quality violin shop, they should be able to help as well.