klswift

you can make it any size you want as long as your hand can fit in. But, having said that, if you want it to be the whole opening, figure an 1" narrower than the opening. To give it a finished look and to make it secure at ends, you will be attaching a small tab on each end. This tab is what is sewn into the sides. So a 9" full side would end up with an 8" zipper opening.

dsch

Thanks to all for their help & suggestions. I'm not sure I'm ready to buy zippers by the yard, yet. So, to klswift, the rule you gave me is helpful, but haven't installed a zipper using the tab method. I used a pattern piece from another pattern & installed the zipper using that. Formula: if my bag opening is 17" then I make the zipper 18" or would 18 1/2" be better since the ends will be recessed & tucked inside? I just don't want it to be too short nor too long.