Measure it by lungfulls, not "rocks" since it can vary greatly in potency. One big hit (full lungful) of good crack is all you need and it should last you 15-20 minutes if you're a newbie without much tolerance. If you have really good crack, then one big hit can be enough to overdose. When I used to smoke crack I actually preferred getting good crack over great crack because the great crack was too dangerous. I liked the sort of crack where one big hit would give give you a nice bellringer. If you have bad crack you can never get the proper rush because by the time you try to smoke more the first hit will already be wearing off and you'll smoke your entire stash without feeling satisfied.
I should also add crack is not a good road to go down. I'd recommend ordering some coca leaves and just sticking to the natural plant. Crack will drain your bank account fast and give you terrible come downs. It's hard to hit the sweet spot with crack, where you feel satisfied with your high but you're not overdosing. Most of the time you spend smoking crack you will feel unsatisfied, chasing a high you can rarely achieve and going crazy trying to avoid the come down. However, I will admit when you do hit the sweet spot for a brief couple of minutes crack can give you one of the most intense highs on the planet. It's many times more euphoric than IV heroin. But soon after that you'll find yourself crawling around the floor searching for pieces you may have dropped willing to do just about anything for more. I used to actually drop some pieces intentionally so I'd have something to find during my floor searches. You'll also call up you're dealer and try to by more and then often times you won't want it anymore by the time he gets there.
