Under a foot? Usually hatchlings are already a foot long or more. My bp was around 18 inches at 2 months old.

Anyway, there's no definite answer to your question. Like people, all bp's grow at different rates. It depends on genetics, how often you feed, and what you feed it. I'd say as long as you're feeding your bp a mouse or rat 1-1.5 times the thickness of his thickest part, once a week or so, he should grow at a healthy rate. I've had my bp since August 24th and when I got her, she was about 19 inches long, and thick enough to take a small adult mouse. Now she's going on 6 months old, 2 feet long, and the thickness of a banana. Last friday, she ate her first weanling rat with ease. Maybe that can give you a rough estimate of how fast they grow.