How to pick the right zipper length & other zipper tricks
After writing about my Rigel, I received some questions on how to shorten a zipper and what to do when the zipper length you need simply doesn't exist. I'm not going to explain to you how to install a zipper, since there's plenty of information to find on this subject. If you need a good tutorial I recommend this one by Sunni Standing of A Fashionable Stitch on Craftsy.This can be really confusing at first, but here are some tips to get you going! However, first we need to establish something really important:
Basic truth No. 1
Always get a zipper that's either the perfect length or longer.
You can't make a zipper longer yourself, but you can make it shorter. If you are in doubt: get the longer one!
How do you know it's the right length? You always measure the zipper from first teeth to last teeth. You don't take the extra zipper tape into account. So a 35 cm zipper is one that measures 35 cm from top of the zipper (named top stop) right until the bottom of the zipper teeth (bottom stop).
Perfect. With this out of the way, let's go on to shortening zippers!
If you want to shorten your zipper, the method you'll pick depends on what type of zipper you're working with.
An invisible zipper
Invisible zippers are usually shortened at the bottom of the zipper. If you install them into waistbands of pants or skirts: shorten them from the top!
There are two types of invisibles zippers: one with a small 'iron' clamp or bottom stop at the end that you can move up and down and a second one without this clamp.
If your zipper has a little clamp, it's very easy: you simply move it towards the desired length and cut of the excess zipper.
The other variation, you handsew a couple stitches at the desired length of your zipper, forming a new zipper end. Make sure these stitches are thight so your zipper doesn't come undone!
Non-separating zippers
Non-separating zippers can be made in nylon, polyester or metal. If they are too long you can use the same method for shortening them as for the inivisble zippers without the clamp. Simple handstitch a couple firm stitches at the desired length to replace the bottom stop of the zipper and cut off the excess. Make sure you use appropriate materials to cut them of. Do not use your fabric scissors, but use some heavy duty or kitchen scissors for plastic zippers and nippers or wire cutters for the metal variation.
The rule of thumb for shortening zippers is also: if it's for pockets or necklines, shorten from the bottom. If it's installed into waistbands of pants or skirts: shorten it from the top.
Separating zippers
Separating zippers come apart at the bottom of the zipper and are usually used in jackets and coats.
These zippers need to be shortened at the top of the zipper. You can not cut of the retainer box or insertion pin at the bottom (the two little thingies you put into each other to close your zipper) cause if you do so, you can never close your zipper again!
This is what you need to do!
Step 1 Insert your zipper per instruction, starting by placing the bottom of the zipper at the right point. Let the excess zippertape simply flow over the edge of your garment.
Here you can see my Rigel Bomber with a zipper that's too long and coming over the top (the zipper is already sewn in between the bodice front and the facing)
If you need to sew over the zipper teeth, make sure you use your machine's hand wheel instead of going full force. If the needle hits the teeth it will most likely break! By using the handwheel the needle has the time to find it's way through the zipper teeth without breaking.
Step 2 Get your supplies ready: You need your garment and a pair of scissors or wire cutters/nippers if you have a metal zipper
Step 3 Cut of the extra zipper above your stitch line. Make sure you don't cut into the stitch line cause they will come undone. The wire cutter will usually cut through the zipper tape as well. 
Step 4 Turn your garment to the right side and admire your shortened zipper!
You can make sure the ends of the zipper don't fray by putting a tiny bit of fraycheck on them.
Yay! No more zipper worries!
I hope this made all things zippers a bit more clear!
Happy sewing!
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