Basic Pattern Altering

Using existing patterns can be a great way to start a cosplay project, but most of the time the patterns you find don’t quite fit your character.  Luckily, its pretty easy to alter a pattern to fit your needs!


  • Pattern
  • Scissors
  • Pins
  • Paper
  • Pencils
  • Curved Ruler for Sewing
  • Dressform (optional)


Step 1: Cut your pattern pieces out

Since you’re starting with an existing pattern, you’ll need to cut out all the necessary pieces.  Make sure you cut out all the pieces you’ll need according to the size you fit best.

For my example, I’m using the pattern M7071 from McCall’s to make Princess Bubblegum’s dress from Adventure Time.  To use this pattern effectively, I’ll need to alter the collar, sleeves, remove the ruffles, and combine the front and inset pieces into one for “Blouse B” and remove the ruffles on “Skirt C”.

To find your correct size, look at the information on the back of the pattern.  It will give you a list of measurements that correspond with different sizes.  Compare your measurements with the measurements on the list and pick the one that fits best.


Tip:  If some of your measurements fit one size bit some fit another size, go with the bigger size.  Its easier to alter a larger pattern to fit smaller than it is to alter a smaller pattern to fit larger.

Once you have decided your size, cut out all the pieces you need to make your garment(s).  If you’re using a commercial pattern, you’ll be able to find a list of the pieces you need for each garment in the instructions.



Step 2: Decide What You Need to Change

Princess Bubblegum’s dress is very similar to this pattern, but her dress has scalloped sleeve bands, a rounded collar, and does not have any ruffles.



Step 3: Start Altering!

Combining Pieces

In my opinion, the easiest place to start is by combining pieces that should be one.  You may not always have to do this, but with my example it was a necessary part of the process.  The blouse on this pattern had a ruffle going through the chest, which split the garment into two pieces where the ruffles would fit into.  Princess Bubblegum’s doesn’t have these details.  Instead, it needs to be one solid piece.

In order to alter the pattern to fit what we need, all  we need to do is lay the pieces overtop of one another and pin them to fit. As you can see below, I have combined pattern pieces 10 and 13.



Optional Step: Pin Your Pattern Pieces Together

This is not a necessary step, but I find it helps to pin all the pattern pieces I can together as if they were sewn and pin them to my dress form to give myself an idea of how the finished garment will look.  If there are are darts, I pin the darts.  If there are seams, I pin the seams.  Get it as close to a sewn garment as you can!


Changing Pieces

Some of the pattern pieces themselves will need to be altered to fit your costume.  To make the scalloped sleeve bands on Princess Bubblegum’s dress, we’re going to start with the original sleeve band piece and use it to make a new pattern.


First, fold it along the fold line to get the correct size.  The pattern is meant to have one piece of fabric cut per sleeve, and those pieces of fabric to be folded to make each band.  Since I needed scalloped bands, I’ll need to cut two pieces of fabric per sleeve and sew them together to achieve that scalloped look.


Then, grab a piece of paper (any paper will work) and start drawing your new pattern according to the size of the original. I simply put the original pattern over my paper and traced around it.  Be absolutely sure to add in ANY seam allowances you need!  The seam allowances are so important!  if you don’t include them, your patterns won’t work!

Also alter the size of your bands at this time if you need to.  For Princess Bubblegum’s sleeves, the bands needed to be longer than the original band, so I lengthened the width of the pattern to 2 inches. I also marked out where the scallops would go.  I decided that since the length of my band was exactly 12 inches, I could easily make 4 scallops fit perfectly and symmetrically into the length.

Once I had everything mapped out, I used a curved ruler to get the perfect curve for those scalloped edges.


I also always take the time to write important information on my new pattern pieces, such as how many to cut from fabric/interfacing, where the seam allowances are, and where the center is if it is applicable.


Adding Pieces

Sometimes you’ll need to add additional pieces to the garment to fit the character.  The collar on the dress pattern is just  a simple band around the neck, while Princess Bubblegum’s collar folds over and has a rounded front.  To make the collar more like Bubblegum’s all we need to do is add a piece to the band that will fold over.

Start by taking the original collar pattern and use it to trace a copy onto a sheet of paper. Then, add in your curved areas at the center front.  A curved ruler makes this easy once again!


Be sure to also take into consideration how the new piece of the collar will fit in with the original patterns.  The original collar was mirrored over the center front, but this new piece won’t actually connect in the front.  It will be two separate pieces on each side, so we need to add in a seam allowance to the curved edge to account for this.


If you’ve taken the time to pin your pattern pieces together, you can add the new piece on to your existing patterns to see how it will look!  Remember that the piece also includes the seam allowance, so it will look a bit larger than it actually will be.


Add, subtract, change, and replace until you’re done!

You can continue to alter pieces, add pieces, and take away pieces as needed until you have a perfect pattern for your costume.  For example, I could add more fullness to the skirt by adding more material at the sides.  I could also shorten the length by of the skirt by simple folding the pattern up and pinning it at the length I wanted.   I could even give the hemline a different shape if the costume called for it.  Its all a bunch of experimenting until you find what works for you, so have at it!


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