It also depends on the sex. Males are usually 1.000-1.500 gram when they're fully grown. And females are usually about 2.000-2.500 gram. But as already said, it depends on the snake. The biggest bp ever recorded weighs 8.000 gram (not a hybrid but a bp). But this is very unusual. The biggest I personally know about is around 4.000 gram, which belongs to a friend of mine.