How to Make a Full Bust Adjustment on T-Shirts (No Darts)

A bust adjustment on T-shirts is worth the effort, and it’s not as intimidating as you might think. You’ll end up with a supremely better-fitting knit shirt, and you’ll feel like an absolute boss for understanding how to execute a full bust adjustment with no darts.

This post covers how to do a full bust adjustment without darts for two types of T-shirts: T’s with set-in (aka, separate) sleeves and T’s with dolman (aka, grown-on or kimono) sleeves. Yep, it’s a two-for-the-price-of-one deal in Sie Macht blogland! That’s because most of the steps for a dartless full bust adjustment are the same.

Let’s answer some of the bigger FBA Q’s before diving into a step-by-step illustrated full bust adjustment tutorial.

What is a Full Bust Adjustment?

A full bust adjustment adds width and length to a front bodice pattern piece. It’s a combination of slashing — cutting the pattern pieces — and spreading — pulling apart the cut edges. Oh yeah, there’s some dart stuff in there, too. (Sounds scary but is cool-slash-fun, promise!)

Why Do a Full Bust Adjustment?

A full bust adjustment helps clothes better fit your body. If you’ve suffered through any of the following, an FBA may be in order:

• Gaping in button-up shirts
• Prominent pull lines between breast apexes
• Too-big shoulders when the bust is OK
• Loosey-goosey armholes
• Immodest wrap tops
• Front hem that’s too high (in an annoying way)
• Neckline gaping
• A fabric wrinkle (like a wannabe dart) in your armhole above your bust

Cups are Confusing

Get ready for a crash course on BUST CUPS.

In sewing pattern drafting, cup size is determined by the difference between high bust circumference (under the armpits above the breast tissue) and full bust circumference.

In ready-to-wear bras, cup size is determined by the difference between band circumference (under your bust around the ribcage, sometimes called underbust) and full bust circumference.

Most sewing patterns are drafted for a two-inch difference between the high and full bust circumferences. This is a B cup.

The confusing thing is that a two-inch difference between band and full bust circumferences is a B cup in RTW bras.

For the record, Sie Macht pattern sizes are drafted the sewing pattern way: the B size range has a two-inch difference between the high and full bust circumferences, and the D size range (D for a D cup) is drafted for a four-inch difference.

Sewing pattern companies use these differences between high and full bust circumferences for cup sizes:

• 1 inch = A cup
• 2 inches = B cup
• 3 inches = C cup
• 4 inches = D cup
• 5 inches = DD cup
• 6 inches = DDD cup

When to Do a Full Bust Adjustment

The time to do a full bust adjustment is when the difference between your high and full bust circumferences puts you in a cup size that’s bigger than the pattern’s cup size.

And how can you tell what cup size the pattern company drafts for?

• They tell you in the size chart, on its website/social media, or in other text. (Best option.)
• You turn to “sewcial” media and ask the question there. (Better option.)
• You measure the flat pattern pieces and do the math. (Good option.)

If your difference is three inches or greater, I say go for the FBA. If your difference is less than three inches, it’s more about your fit pickiness and comfort; you probably can get away without an adjustment.

I designed Cass, Sie Macht’s T-shirt pattern PDF, for minimal adjustments. With a T-shirt like Cass, which has a ton of design ease, breasts of many sizes can get by without a full bust adjustment.

Keep in mind that all adjustments are a matter of personal preference. They’re your clothes, and they can fit however YOU want them to. There are “standards” for good fit, and pattern designers have a fit in mind, but it’s always your call, sewist.

How to Do a Bust Adjustment on T-Shirts (Dartless FBA)

Step 1: Discover Pattern Cup Size

Use the tips I dropped in the previous section to learn the pattern cup size. And don’t forget that you always can drop a line to the pattern company via social media, email, or whatevs to get the cup size, too. This shouldn’t be classified information!

Step 2: Discover Your Difference

Measure your high bust circumference. Measure your full bust circumference. Subtract your high bust from your full bust to get your SEWING cup size.

Full Bust – High Bust = Cup Size

Now we need to learn the difference between the pattern’s cup size and YOUR cup size.

Let’s say the pattern is drafted for a B cup and your cup is a C (3-inch difference between your high and full bust circumferences — see bullet list above under “Cups are Confusing”).

Your Cup Size – Pattern Cup Size = Amount of Full Bust Adjustment
EXAMPLE: 3 inches – 2 inches = 1 inch

Because you’re making an adjustment on one half of the front of the sewing pattern, divide the amount of the full bust adjustment in half.

Amount of FBA ÷ 2 = Horizontal Adjustment to Pattern Piece
EXAMPLE: 1 inch ÷ 2 = 1/2 inch

In a few clicks we’ll be slashing and spreading like animals, and that horizontal adjustment to pattern piece measurement will be VERY important!

Step 3: Trace Off Bodice Front

Call it the risk-averse move. Preserve the original version of the front bodice piece in case something goes sideways. RELATED: Tracing Sewing Patterns: How I Attack My Least Favorite Sewing Task

For a full bust adjustment, you’ll need extra paper and tape to patch slashed and spread areas in the pattern. Get yourself a pair of (not fabric!) scissors or a craft knife and a ruler/straight edge. I also suggest markers of different colors to easily track your work and make labels. (Nice, but not necessary.)

As I did the following illustrations, I tried to make the pattern pieces look the way they’re going to look as you follow along. That means there’s going to be a lot of odd paper patches, Scotch tape, and lines bent in weird ways. In short, it’s going to look like a hot mess.

I could have made each illustration look neater and less visually busy. But, it was important to me that I showed EVERY step, because when you do your own FBA, it’s going to look bananas, too, and that’s OK. You’re on the right track.

Step 4: Start without Sleeve

All my research indicates that FBAs are made with sleeveless front bodice pattern pieces. I’m going to show you how a dartless full bust adjustment looks for a set-in sleeve pattern and for a grown-on (aka, dolman or kimono) sleeve pattern — such as Cass. The grown-on sleeve front pattern piece is the Cass front pattern piece.

The easiest way I’ve seen to remove a grown-on sleeve is to lop it off, straight up and down. Taking off this type of sleeve is an art, not a science; don’t overthink it.

Step 5: Mark Bust Apex

This doesn’t have to be perfect. Hold up the pattern piece to your body and make and educated guess. (Hint: Your apex (probably) is the nipple, if you’re looking for a landmark.)

With the Cass T-shirt, the shoulder seam IS NOT on top of your shoulder. I suggest gently taping together the front and back pattern pieces AT THE SEAM (not the pattern piece edges) and draping this half shirt over your body to see where your apex is.

Step 6: Draw Line from Bust Apex to Hem

Make this straight line parallel to the center front. The line should be perpendicular to the hem.

Step 7: Draw Line from Bust Apex to Armscye

Draw a straight line about one-third up the armscye.

Step 8: Draw Line from Bust Apex to Side Seam

This straight line goes about where a dart would live if there were a dart in this dartless shirt.

Step 9: Draw Line from Center Front to Vertical Line

Draw this straight line about 3 inches from the hem. It should be perpendicular to the vertical line between the bust apex and the hem.

Step 10: Slash from Hem to Bust Apex to Armscye

Scissors time! Cut along the vertical line to the bust apex. Pivot at the bust apex and cut along the line to the armscye. DO NOT cut all the way through the armscye. Leave a hinge (1/8 inch).

Step 11: Slash from Side Seam to Vertical Line

Cut along the line from the side seam to the vertical line near the bust apex. Leave a hinge here, too!

Step 12: Slash from Center Front to Vertical Line

Cut the line from the center front to the vertical line. Cut all the way through the pattern piece. (Feels good, doesn’t it?)

Step 13: Mind the Gap

This is why hinges are important. Spread the vertical line HALF THE DIFFERENCE between your high and full bust measurements. Up top we called this the horizontal adjustment to pattern piece. (See Step 2: Discover Your Difference.)

I like to play with the armscye hinge first, swinging down to make the tip/hinge of the newly-emerged side seam dart as far from the vertical line as the horizontal adjustment to the pattern piece. Then I play with the side seam dart hinge to make the sides of the slashed pattern pieces parallel.

Patch the side seam dart and horizontal spread with paper and Scotch tape. You don’t have to tape down the cut-free lower-center-front piece just yet (that’s coming next!).

Step 14: True Hem

Slide the rogue lower-center-front piece down so it’s even with the hem. Patch gap with paper and tape.

Step 15: Redraft Side Seam Dart

The dart legs need to point to the newly moved busts apex, so move ’em!

Step 16: Cut Out Dart

Take a scissors to the dart and make some negative space! In this illustration, I also tidied up the paper patches.

Step 17: Slash from Hem to Bust Apex

Cut straight from the hem to the bust apex, leaving a hinge.

Step 18: Close Side Dart

Put the hinge to work. Swing the the lower dart leg up to touch the top dart leg. Tape. You’ve moved the dart to the hem, and the side seam has swung out.

Step 19: Patch New Gap

Get some paper in there to support this mauled pattern piece. I used a slightly different color for this piece of paper.

Step 20: Draft Yet Another Dart

We’re gonna swing the side seam back toward the center front by making and closing another dart.

Make a mark about an eighth of the way up the armscye (it doesn’t have to be exact). This mark is the point of your new dart.

Draw dart legs from the hem to the mark.

Step 21: Cut Out Dart

YEAH, cut out that dart, but leave a hinge at the dart point.

Step 22: Swing Dart Closed

Swing the side-seam section toward the center front to close the dart. Tapey-tape that gap out of existence.

Step 23: Pretty Up Hem

The hem is uneven. Patch with paper and tape. Draw a thoughtful hem from the center front to the side. (You also can pretty up the set-in sleeve T’s side seam here, too. The final illustration provides guidance.)

Step 24: Add Back Sleeve and Draw New Shoulder (Grown-On Sleeve Pattern)

OK, if you’re living that grown-on sleeve life with Cass (or a similar pattern), the bottom of the sleeve touches the bottom corner of the armscye. The top of the sleeve will bump the shoulder.

Put a piece of paper under the sleeve/shoulder area. Draw a new shoulder from the neck to the tip of the sleeve. (You also can pretty up the grown-on sleeve T’s side seam here, too. The final illustration provides guidance.)

Step 25: Check Seams (aka, Perform Due Diligence) (Set-In and Grown-On Sleeve Patterns)

You’ve adjusted seam lengths to the front bodice through this process. But, a front bodice pattern piece does not exist in a vacuum.

Walk or measure the following SEAMS (not pattern piece edges):

• Front bodice side
• Back bodice side
• Front bodice shoulder (grown-on)
• Back bodice shoulder (grown-on)

The shoulder seams *should* be close to the same length; same for the side seams.

Here’s how the bust-adjusted pattern pieces look all prettied up! You can see how the shoulders, armscyes, and sleeves didn’t change (much), but we gained length and width, specifically below the armscye.

And that’s all there is to a bust adjustment on T-shirts! HA, yes, I’m being funny (trying to be funny).

It’s a lot of steps, true. But, a well-executed full bust adjustment with no darts will make any T-shirt pattern more comfortable to wear. What’s more, you’ll feel more confident wearing your bust-adjusted T, because leveling up sewing skills is great for self-esteem.

Over to you, sewist: Have you tried a full bust adjustment (dartless or otherwise)? Did you know all that stuff about sewing cups vs. RTW bra cups? Have any hot FBA tips to share? Please sound off in comments! Thanks for reading.

ALSO: Would you be interested in an ebook on this topic? Please LMK in the comments! TY!

P.S. Check out these posts to help you sew your very best Cass:

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