How to Make RTW Pants Adjustable Waist

In the past I have made pants for my kids with an adjustable waist. When making pants it is a lot easier to do, but what if you bought pants that need an adjustable waist? I have two pairs of jeans that need an adjustable waist, my waistline fluctuates and it helps to have a good fit all the time if I can adjust the waist. It also is great for people trying to lose weight, you won’t have to buy new pants every time you lose a few pounds or wear sweatpants all the time.

So how do you make Ready-to-wear pants into adjustable waist pants? Here is how I did it.

Step 1

You first need to exam the waistline of the pants. You are going to need to feed elastic through the waistband and if the waistband has stitching anywhere along the way (like a seam that goes through all layers), then you might not be able to feed the elastic through. If you can’t feed the elastic through the waistband then those pants can’t have an adjustable waist.

Step 2

You will need to get some buttonhole elastic. If you go to your local store you might find they don’t have it or they only have Dritz buttonhole elastic. However the Dritz elastic is only 1/2″ (and not a very good elastic) and you will most likely need a wider elastic. To determine what size elastic you need measure the waistband height (from top-stitching to top-stitching if it has it).

Not all buttonhole elastic is created equal. To tell if you have good elastic, stretch it to it’s max. If it curls or weakens then it’s not good elastic. Also washing a scrap of elastic is a good idea. This will tell you how much the elastic shrinks when washed and how it holds up. The buttonhole elastic is going to be exposed when it is washed which causes more wear. If you don’t use good elastic you will need to replace the elastic after a few washes.

Step 3

Now that you have chosen some buttonhole elastic you will need to choose some buttons. You need two button that are smooth (you don’t want the buttons to be digging into you) and fit the button holes well.

How do you know what size buttons to use? You want a button that it a little larger than your button hole, to small and the button will not hold the buttonhole elastic in place, too big and you will have trouble buttoning the elastic. The best way to find the right button is really trial and error. Pick a button and push it through the hole. If it was too hard to push it though that button is too big. If it was too easy than that button is too small. You want to take some effort to push it through.

Step 4

Now it is time start working on your pants. You need to decide where to place the slit for the elastic and the button. This is more personal preference. If you want just elastic in the back you can put the slit and button on the side of the pants (be careful about your placement, you might want to put it slightly to the front, directly on the side will most likely be uncomfortable). I like to sew the buttonhole behind the first belt loops so I can sew through all layers, for a more secure button, and not have the threads visible. I put the slit right next to it about 1/2″ away.

You will want to mark a line for the slit that is slightly longer than your elastic width. I used chalk to mark my lines. I also marked where the button will go. Once your line is marked and you are sure that is what you want, then will need to cut a slit through only the inside layer of your waist band along that line.

I recommend finishing the edges of the slit. I used fray stop and stitched a hand-stitches buttonhole. This will keep if from fraying during use and washing. At first I just did the hand-stitched buttonhole but my denim kept fraying more and more as I worked. The fray stop helped with this and made it easier to stitch.

Step 5

After you finish making the slit, you should sew on your buttons. You will want to do this before feeding the elastic through the waistband. It gives you a place to attached the elastic to while feeding through the waistband. You can sew it on any method you like as long as it is very secure. This button will be under a lot of stress and you won’t want it falling off during wear.

Step 6

Preparing the elastic. Not you will need to cut the elastic to length. I recommend measuring the elastic on you. I measured a length around my hole waist and stretch it slightly. Then I cut it. This might possibly be longer than you need but you can always shorten it.

After you cut it you will want to finish the edges. I recommend turning it like a hem and stitching it in place. This can be done on a sewing machine. It creates a nice finish that won’t be itchy later on or unravel.

Step 7

Now it is time to feed the elastic through the waistband. Take one end and button it on one of the buttons. Take the other end and feed it through the waistband, keeping it flat and untwisted. I prefer using a safety pin to feed it through the waistband but you can use whatever method you prefer. One you get it through the other slit, you can button it to the other button.

Try on the pants and adjust the buttonhole elastic to the tightness you want. If you have too much elastic you can fold it over and button it to the button again. I don’t recommend cutting it shorter just yet. Wear it and wash it to make sure that you want to shorten it before doing to. The elastic might shrink a lot or maybe you decide it is too tight after wearing it and you need to loosen it. It might be a good length after wearing and washing.

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