Bin Boundaries

#1
Hey Everyone!

I just have a quick question when calculating my bin and frequency.

I have a Max of 4.144%, Min of -3.733%. I want to a good amount of bins (around 15-20)

This is what i have done so far 1) rounded up my max and mins to 5% and -4%. 2) I calculated my bin as 4.144% - 1% = 3.144%.
3) divided 3.144% by (9). * where i need the help (if my process is correct) is that the number that i used to divide (9) is that the amount of bins that i am allowed to use?