What kind of hibiscus is it? If it's a tropical hibiscus and you live where it can be planted in the ground, these hibiscus can get 15 feet or more.
I'm going to assume you have it in a pot. As long as you give it enough sun, water and fertilize, (and it's not root bound), it will grow at a decent clip.
If it does get too big, you can control the size by pruning the branches and the roots. Read up on how to do this properly before you try it.
There are past posts on this forum that cover both.
If you need more info and I'm assuming you will, ask away!
Barb

I want to know how big around hibiscus get,