You can usually find great deals on zippers if you know where to look. You'll find great prices and great colors, but usually not the lengths you want. eBay is a great place to get inexpensive zippers in bulk, but how to you plan for future zipper needs without knowing what sizes and colors you'll want? Knowing how to shorten a zipper will help you save money. This Instructable gives you a quick and easy method for shortening plastic zippers.
Step 1: BoM
Longer than necessary zippers
Step 2: Measure
Using a ruler and chalk, measure and mark off (on both sides) where you want your new zipper to end. I know I have an upcoming small pouch project and only need a 3" zipper, so I marked off at 3" on a zipper that was originally 9". You could also put a piece of tape here to ensure a straight line.
Don't cut anything yet.
Step 3: Machine Stitch
The little metal bar at the bottom of the zipper is the end point. Zippers don't zip past this bar. We're going to recreate this bar by putting in a couple of stitches to hold the zipper sides together. I used a simple straight stitch and went back and forth over the zipper a couple of times. You can use whatever stitch you prefer. The bars also don't need to be as long as I made them. Also, unless your zipper is going to be visible, thread color doesn't matter.
Step 4: Hand Stitch
You may prefer to hand stitch your bar, which works perfectly well and might even be less hassle than using a machine. Simply thread a needle and being stitching around the zipper bars several times. When you're satisfied, cut and secure the thread.
Step 5: Trim
Now that you have your "bar" in place, it's safe to trim the zipper to the length you want. Trim about 1/2" down from the new zipper bar. If you want to be really fancy you can use a pair of small, sharp scissors to cut the little triangular fringe onto the end of your new zipper. Either way it's a good idea to add a little Fray-Check to the ends.