Here is the "Crash course" of what you can expect for an answer:
That question has been asked here a few times here, and each time, there is debate. Lots of claims, but not a lot of verification.
The PPeH says that 1 100ml bottle is "enough to provide a peaceful death", and to gulp it down in a few swallows. That Nitschke says he is unaware of people surviving 6 grams. Others claim that they have witnessed the dangers of "under-dosing".
There's also this:
"In the vast majority of cases, one bottle (100ml @ 60mg/ml) of veterinary N will always be satisfactory and lead to a peaceful death, usually within 1-2 hours. [You'll be asleep long before that, though.] However, there is a small group (estimated at <1%) who may exhibit a prolonged comatose phase before death (sometimes up to 24 hours). Outright 'failures' remain extremely rare. Indeed, all of the reported failures investigated by Exis were associated with early discovery and subsequent medical intervention. "
Others say that only applies to sick or elderly people, that more is needed for a strong, healthy adult.
For some, alchohol issues may affect the liver, which will affect the outcome (and more N will not necessarily mean better success.)
Others say it depends on body weight. The average claim seems to be 185-200 lbs and over would need 2 bottles.
Others say that 1 is probably enough, but 2 bottles just to be safe.
The confusing issue is that official assisted suicide organizations tend to use 9-15 grams as their standard. But they have access to the means, whereas for the average person, obtaining it is most likely illegal and expensive. So, 6gm is the bare minimum one would need, while more than that can be hard to obtain, but will speed up the process.
(There's also the issue of pisobental vs. dolethal, which is different in volume. But the same standard concept applies, proportionately.)
Hope this helps.