How To Resize A Button Up Shirt

How To Resize A Button Up Shirt

I’ve got to make Bella a pirate shirt for her Halloween costume. (Watch me work on this years’ costumes!) I don’t feel like spending a lot of time or money on this part of the costume. It won’t show much under her vest anyways. I asked around and a friend gave me a shirt to mutilate. It’s an adult size small. I like the sleeves, they’re already sort of piratey.

(In this photo, I’ve sliced off the collar. I plan to add some lace there.)

First, remove your sleeves. This shirt is serged inside, so I used scissors. If you have “invisible” seams, use your seam ripper instead. Do not hack through both layers. Make a small incision, then carefully work your way around the sleeve. The front of the sleeve is shaped differently than the back, and you’ll and up with part of the shirt attached to your sleeve. If only I listened to my own advice.

Mark your new cutting lines. You can accomplish this by pinning while wearing it (if it’s for you) and then marking. A real seamstress or tailor will use a hip curve to draw a nice clean line. If its for someone else, have your victim put on the shirt inside out, then mark it. Do as I say, not as I do. I’m just eyeballing it since Bella’s in school. It’s very important that you make sure your seams match, and leave some slack for a seam allowance.

DO NOT fold your shirt in half and cut both sides at once ( like I’m about to do.) it’s extremely important that your sides match. Get out your ruler and get it right. Tailors chalk is nice here, since it’s easy to remove if you need to adjust your lines. I use the Singer disappearing ink fabric pen. A touch of a steam set iron removes it quickly and easily.

Here, I’ve cut off the side seams. I adjusted my sleeve opening to make a smaller hole. I cut a little at a time until it looked right. Again, I just eyeballed it, which is WRONG. Im being very, very naughty. You can use a good fitting, similar shirt for reference. An armcye is a specialty drafting tool for sleeve openings. I haven’t seen mine in years.

Now, your sleeve will be bigger than your sleeve opening. We will have to ease in the fullness to make it fit. There are several ways to do this. We can do a puffed or gathered sleeve, or stitch a placket or dart. Since this is a pirate shirt, I’ll go with a gathered sleeve.

Let’s mark your gathering line. They will go along the shoulder curve as seen below.

To sew a gathering stitch, set your machine to the tightest tension, and the longest stitch length. On my Singer, that’s a 9 for tension and a 4 for stitch length. You will sew from your starting point to the ending point that you marked. Do not back stitch. Leave a few inches of tail on all your threads. Your gathering stitches will be removed later. You may use a different color thread if you wish. This will make it easier to see. It’s really easy to accidentally seam rip your actual stitch line rather than the gathering stitches.

After pinning, we’ll tightly hold one of the threads while gently tugging our fabric, creating gathers like this:

But don’t pull your gathers yet. First, match up your armpit seams. I put X’s on the armpit seams below. Just in case I lost ya. ( I’m sure there’s a technical name for armpit seams. Who cares.)

Make sure your sleeve and shirt have their right sides facing each other. (Right sides meaning the part that shows when you are wearing it.) Nothing like sewing a sleeve inside out! hang on, I’ll show you how to tuck your sleeve inside the shirt. It’s easy. Don’t be scared.

My shirt is inside out, and my sleeve is right side out. See how I lined up the armpit seams? Basically, I made the X’s kiss. Then I pinned them. Now they are stuck together forever. They better learn to get along.

*A note: you are most likely sizing an adult size shirt down to a smaller adult size. Since I’m sizing and adult shirt down to a child size, I had to lengthen my gathering stitch line on both sides. This is because I have to make an adult sleeve fit into a child sized armcye. So, my gathers will be obnoxious and probably kinda ugly. Yours will just have a slight gathering at the top of the shoulder. Mine might have to go all the way around. It’s just much faster than me making a whole pirate shirt. Plus, free is the right price for a shirt that will only be worn once.

Next, we will pin the center of the sleeve cap to the shirt shoulder seam. See below.

Now we pin around, pulling gathering stitches to fit. You want your fullest gathers at the top shoulder seam, easing into smaller gathers. Make sure you have a nice, tight fit.

Stitch it up. Rinse, lather, and repeat for your other sleeve. Remove your gathering stitches using a seam ripper. See the purple thread? This is where different colored thread comes in handy.

I sliced off 4″ from the bottom, leaving a 1 1/2 seam allowance. You probably won’t need to change the hem. I have to because it was WAY to long for Bella.

I’m not hemming it since I still have to add pirate details. I’m adding lace around the collar and sleeves, and a small slit in the back for ruffles. The ruffles will cascade down the small of her back and curve around following the hemline sort of like this:

(It will have a bow with long tails and her pirate tutu will be peeking out from under the bow. I absolutely have to tell you the details.)

For tutorial purposes, I’m stopping here. This is the finished product.

I hope someone finds this useful! It probably takes longer to read the tutorial than to actually do it.

About The Author

Amy Mayen

Hello. I'm Amy and I'm addicted to sewing. I borderline-hoard fabric, buttons, & patterns. Sometimes I wish I could pile my fabric up on the floor and just roll in it!


  1. Charleen

    Great job! You added simple to follow photos to great instructions!

  2. Notkirstyallsop

    If only all sewing tutorials were like this 8-) Thank you, I’ve got to try and resize an adult boiler suit to a kids one for Halloween costume. Yes the adult one was the right price whereas kids costume version must have been made with diamond thread and unicorn hair. What could possibly go wrong.


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