PMI doesn't tell us how many questions must be answered correctly in order to pass. All we are told in the PMP Credential Handbook is that "The passing score [&] is determined by sound psychometric analysis."

So how do you get around the catch 22 situation of wanting to know when you are ready, when nobody tells you what "ready" really means? My recommendation is to apply the 85% rule as follows:

Keep track of your score as you answer PMP Exam sample questions. If you consistently answer at least 85% of sample questions correctly on your first attempt (subsequent attempts don't count), then you can probably consider yourself ready for the real exam.