Keep in mind that female Common Boa Constrictors are bigger than the males, and usually heavier. The average adult female will be between 8 and 9 feet long, and about five inches across her back at the widest point, unless either pregnant or digesting a recent meal. A male will be somewhat smaller. I've seen females as large as 11 feet, but that's an old, old snake, and not common at all. I've kept and bred Boas for the past 30+ years, so this is based on long-term personal observations of my snakes and those of others who breed this species.