Hi, to be honest this is my first time to make this plastic bag. what I did is I cut a 22 x 22 cream fabric and put pleats and fit my hand where I can put it easily on the top but at the bottom I put the plastic bag that I tied into a ball and look if it will fall down on the floor if not it means I got the right hole for it. I just eye balling it. i'm not a professional seamtress more on just trying to make things. If there's anything I can do help you just be free to ask.