Discover how to slash off the hem of a Cass T-shirt - or any T-shirt - and replace it with a flounce.  The flounce changes the silhouette of this relaxed-fit T-shirt in a fun and floaty way that might inspire you to give this hacked garment a big, ol’ twirl.

In this post, I’m showing you how to slash off the hem of a Cass T-shirt — or any T-shirt — and replace it with a flounce.

The flounce changes the silhouette of this relaxed-fit T-shirt in a fun and floaty way that might inspire you to give this hacked garment a big, ol’ twirl.

Keep reading to discover how to draft a flounce pattern and for tips on how to sew a flounce to a T-shirt.

Speaking of drafting a flounce, I made you a PDF worksheet (keep reading!) that you can use to draft a flounce pattern piece of ANY size for ANY garment. There are illustrations to help you understand what we’re talking about (i.e., math, locations) at every point.

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I attached the flounce to this T-shirt near my high hip.

Planning the Cass Flounce Hem Hack

My vision was for a flirty, short Cass T-shirt dress with a flounce, and I wanted to keep the seam that attaches the flounce low. I used a croqui of my body (created when I did a body type analysis) to sketch the Cass + flounce on my figure and determine the best place for the flounce seam.

The hack you’re looking at places the flounce around my high hip (for a quasi-dropped waist “Great Gatsby” moment). (To make the hem straight, I cut off the curved part of the Cass hem from side seam to side seam.)

When you sew your flounced T-shirt, you could easily place a flounce under the bust for an empire waist, or put the flounce at the natural waist and keep the garment T-shirt length. Flounces can be as long as you want them to be; you’re the boss. They’re fun to use to play with proportions.

Whatever you decide, know that flounces bring the drama (see: Flounce Sleeve Dress Hack Tutorial). So, prepare yourself for fun with movement and volume.

The flounce on this T-shirt is 11 inches. It's probably the shortest I'd want this flounce. This dress is short.

Dress Fabric

A word about this knit fabric: It’s a mystery fiber fabric! I’m sure it’s polyester to some degree, because of the way it feels and presses. It’s not particularly stretchy, either (almost verging into double-knit territory). It reminds me of the fabric in this post: Striped Cass T-Shirt and New Ginger Jeans.

I came by this fabric in an unusual way. My Milwaukee sewing pals and I took a little roadtrip to check out a fabric stash. The textiles belonged to an enthusiastic home sewist who passed away, and her husband was trying to re-home her sewing stuff.

Even though this wacky jungle print features colors that I don’t normally wear (or believe I look that good in!) I was instantly attracted to it. So, I took it home.

I thought I was going to make a Butterick B6051 maxi dress with this fabric, but when it came time to stitch a flounce-hem T-shirt, I couldn’t wait to cut into it.

Here’s a hot shopping tip for you: When you see a listing on Facebook Marketplace, Craigslist, rummage sale, estate sale, etc., selling sewing stuff as a single lot, reach out to see what the story is. There’s a chance the seller doesn’t know much/anything about sewing and is trying to get rid of a stitching collection all at once because they feel out of their depth.

You *might* be able to convince the seller to separate the goods if you have sewing friends (probably IRL sewing friends) who’d be willing to buy a chunk of goodies, too.

Check out the PDF worksheet to draft your own flounce for a sewing pattern.

What You Need for the Flounce Hack

Here are the sewing supplies you’ll need to sew your own flounced Cass T-shirt:

Cass sewing pattern

How to Draft a Flounce worksheet (click link to view)

Paper for pattern work

Writing implement


Compass or other circle-drawing tool



Scissors or craft knife for paper

Washed and pressed fashion fabric


Sewing machine or serger/overlocker


This wacky print makes a sassy flounce T-shirt dress.

How to Draft a Flounce Pattern Piece

0.) Print and assemble the PDF pattern.

1.) On the back pattern piece, determine the location of the flounce seam. Draw a horizontal line across the pattern piece at that spot. The line should be perpendicular to the center back. For the pictured T-shirt dress with a flounce, I drew a line at the bottom of the side seam (not center back).

2.) Place the front pattern piece on top of the back pattern piece with sides aligned. (The sides are the same length.) Using the back pattern piece as a guide, mark the flounce seam on the front pattern piece with a horizontal line. (BTW, these horizontal lines are your slash lines.)

3.) Sometimes the FRONT pattern piece is longer than the BACK pattern piece at the center front (for example, this happens with the D Range Cass). The extra length in the front is to accommodate greater bust volume.

With sides still aligned, measure the difference in center length between the front and back pattern pieces. Put a mark below the FRONT horizontal slash line that’s the measured distance.

For example, if the front pattern piece is 1 inch longer than the back pattern piece (comparing center front to center back), make a mark 1 inch below the horizontal slash line. Connect the start of the slash at the side seam to the new mark below the slash line. (Don’t worry, the hem will still be straight as you wear the garment.)

4.) BEFORE you slash front and back bodice pattern pieces, draw a parallel line ½ inch BELOW the slash line. This is the seam allowance. Slash this NEW line on both pattern pieces. (P.S. You can make the seam allowance any length; it’s ½ inch in the pictured dress.)

5.) Grab the flounce worksheet PDF. We’re going to start filling it out, starting with (i). We gotta do a bunch of math to generate pattern dimensions BEFORE we can draft the flounce pattern piece (aka, draw a donut).

Measure the width of the front and back bodice pieces at the slash, NOT including the side seam allowance (when you attach the flounce, the side seam.will be sewn = no seam allowance).

For my Cass flounce T-shirt dress here, the front pattern piece measured 10.25 inches and the back pattern piece measured 11.25 inches. We’re going to multiply each measurement by 2 (because the pattern pieces are cut in HALF) and add the doubled measurements together.

(10.25 x 2) + (11.25 x 2) = 43 inches

= Circumference of (Flounce) Inner Circle

= Upper Flounce Seam

6.) Now we need to calculate the radius of the inner circle at (ii). (In case you hadn’t guessed, each calculation grows on its predecessor.)

Continuing with the math from my flounce dress:

Radius of Inner Circle =

Circumference of (Flounce) Inner Circle ÷ (2 x π) = 

43 ÷ 2π =

6.8 inches

7.) Looking at the worksheet, you can see that (iii) in the diagram is the length of the flounce, i.e., the distance it’s going to drop from the seam. (This length doesn’t include seam or hem allowance.) Choose your flounce length.

I set my dress’s flounce length at 11 inches. Proportionally, it’s a great length for the dress and my body. But — when I got in my car for the first time wearing this dress, I was a little surprised by how much seat I felt on the back of my thighs. Just sayin.’

8.) Let us calculate the radius of the outer circle (iii).

For my dress:

Radius of Outer Circle =

Radius of Inner Circle + Flounce Length =

6.8 + 11 =

17.8 inches

9.) And, just because we’re on a roll, let’s calculate (iv), the circumference of the outer circle. Technically we don’t need this measurement to draft the flounce pattern piece, but I think it’s useful to see how long the edge of a circle is. For example, if you want to finish the edge with bias binding, you need to know the circumference.


Circumference of Outer Circle =

2 x π x Radius of Outer Circle =

2π x 17.8 =

111.8 inches

10.) Ready your pattern paper, compass, ruler, and writing implement, because it’s finally time to draw the (half-)donut pattern piece. We’re drawing the outer circle first. Draw a line that’s the length of the outer circle diameter (2 x radius). Mark the center of the line.

In my case, that’s 35.6 inches (2 x 17.8).

11.) From the center, draw a perpendicular line that’s the length of the outer circle radius.

For the example, that’s 17.8 inches.

12.) Place the compass (or other circle-drawing tool) at the center of the outer circle diameter. Use the perpendicular radius line to adjust its spread.

If you're not twirling the flounce on a T-shirt dress, what are you even doing? It's the best.

13.) Using the compass, draw a half-circle from one end of the outer circle diameter line, to the perpendicular radius line, to the opposite outer circle diameter line. Congrats, you’ve drawn the outer edge (“bottom”) of the flounce.

14.) Now we’re going to do the same half-circle-drawing business for the inner circle. From the center and on top of the outer circle diameter line, draw the inner-circle diameter — i.e., draw the inner-circle radius atop the diameter line to the left and right of the center.

The pictured flounce dress has an inner-circle diameter of 13.6 inches — 6.8 inches left and 6.8 inches right.

15.) Coming straight out of the center, draw the inner-circle radius atop the perpendicular radius line.

The example’s inner-circle radius is 6.8.

16.) Again drop the circle-drawing tool on the center and adjust its spread to equal the radius of the inner circle.

17.) Draw a half-circle from one end of the inner-circle diameter line to its opposite end, touching the top of the perpendicular inner-circle radius line on the way. This edge of the flounce attaches to the T-shirt hem. It’s the inner edge (“top”) of the flounce.

If everything has gone according to plan, you should have a half-donut flounce pattern piece.

18.) Add seam and hem allowances to the flounce pattern piece. The Cass T-shirt has a seam allowance of ½ inch, so for my example I added ½ inch to the inner edge and ½ inch to the outer edge. Only the curved edges need allowances, not the flat edges (because the flat edges are placed on the fold when cutting fabric.

19.) On the pattern piece, write “Cut 1 piece on fold” and add double arrows to the flat edges. Cut out the pattern piece along the allowance lines and flat edges.

Drafting a flounce for a T-shirt dress takes a bit of circle math. Check out the PDF worksheet for help.

How to Sew a Flounce to a T-Shirt

1.) Cut out fashion fabric on the fold. Yes, you’re cutting out a fabric donut. Flounces, because they’re circles, are cut on the bias, grain, and cross grain. In other words, don’t worry too much about flounce pattern piece placement in relation to the grain (especially for knit fabric, which often doesn’t fray).

2.) Snip the flounce’s inner edge at quarters. You’ll use this to align with the T-shirt body.

3.) Sew the T-shirt as directed, but ignore the hem finish. Should you be interested, there are many articles on the blog about sewing T-shirts (Cass and otherwise):

4.) Snip quarter marks into the bottom edge of the T-shirt.

5.) Right sides together, align the quarter marks of the T-shirt to the quarter marks of the flounce.

6.) Sew the T-shirt-flounce seam. The seam line for the flounce and the seam line for T-shirt are the same length; this isn’t like sewing a neckband where there’s negative ease to pull the neckband in. Avoid stretching pattern pieces, especially the curved flounce pattern piece.

7.) Finish the flounce hem. In general, drapey knits, like the kind recommended for Cass, don’t fray; you don’t have to finish the raw edge of the flounce hem. If you’re hot to finish the raw edge, I suggest sewing a trim to it or serging a rolled hem. I did a four-thread overlock stitch on the hem of this dress; I like how it looks and it’s easy.

You *could* finish the flounce hem BEFORE it’s sewn to the rest of the T-shirt. The benefit of this is that you would have less fabric to rotate and readjust as you did your thing with the raw flounce edge. I made “Finish the flounce hem” the final step because hems often are the final step of a garment sewing project.

The flounce gives this Cass T-shirt dress a lot of fun, breezy movement.

Get Your Own Cass

If you enjoyed this project, you’d probably like learning about even (!) more (!!) ways (!!!) to hack the Cass T. I got you: Check out Sie Macht’s Cass Book of Hacks.

Cass T-shirt call to action

Over to you, my darling sewing dearies: How do you feel about flounces? I’m (obvs) a fan. I love the drama of a good flounce. What’s your fave sewing pattern with flounces? Please share in a comment. Thanks for reading!

P.S. Could you be a sweetheart and share this post, especially the worksheet, on social media? Particularly on Pinterest? This is prime Pinterest content, and it’s a great way to let more sewists know about Sie Macht. TIA for your help!