Rock bass average about 10 inches, they can get larger.
Shadow bass, which are a related species that I keep, average around 8 and generally don't get over 10. They're also better about handling warmer water which is why they're only found in southern regions.
ya as far as i remember rock bass stay under a foot, but they do have a huge mouth and will eat anything they can fit in it. mines about 5", ya the red eyes are sweet.