I don't really think there's a 'normal' mass to length. I think it really depends on how well the snake feeds and how much the owner feeds it. I like to feed my females pretty heavy if they will take it, they get all my leftover rats that the other snakes won't eat and some will eat 2-3 rats back to back. Others are real picky or will fast for a long time or will only take mice. And some go through phases where they will pound a lot of rats and then slow down quite a bit. I think if they all ate like a hungry dog we could control it better LOL. In general though for females they say the more you feed them the more eggs they will produce and the bigger they will get. For males most people usually feed them sparingly to keep them between 1000 - 1500 grams. A lot of times I'll even skip feeding my males, especially the larger ones, at least until they start looking a bit skinny.