What is a Bust Adjustment?

Cup size in sewing patterns is usually not the same as your bra cup size (although sometimes it can be). A lot of pattern companies are drafted based on a B cup block. Coooool, but what does that mean? Sewing patterns measure cup size by taking your Full Bust minus Upper Bust and the cup size is the difference between the two:

A cup = 1” difference

B Cup = 2” difference

C Cup = 3” difference

D Cup = 4” difference

And so on…

Sister Faye Studio patterns are based on an A cup (even though they are drafted for a human with a B cup bra size). I have friends who have a D cup bra size and are still an A or B cup for sewing patterns. Confusing, I know. Most of Sister Faye’s patterns have a fair amount of ease to them so you may not necessarily need to always do a Full Bust Adjustment (FBA) for them to fit well.

Do you need a Bust Adjustment?

Your starting point in determining whether or not you need a FBA is checking the size charts for body measurements and finished garment measurements as this will tell you the level of ease in the garment. If your sewing cup size difference is slightly smaller or larger than what the pattern is drafted for, you will probably be fine with cutting the pattern as-is. If you see that your full bust measurement puts you in a size 22 but your upper bust measurement puts you at a 18, then you are likely a good candidate for a FBA. If the sewing pattern doesn’t include a upper bust body measurement, then you can look at the difference between your full bust and waist measurements. If you are a 24 bust but a 18 waist, then you will likely need to do a FBA. This is why making a toile (muslin sample) is always encouraged!

Math Time!

If you are like me and math blows your mind, things might get a little confusing for a bit. Not to fear, you can do this!

First, take your upper bust measurement and add 1”. This 1” is because you know Sister Faye patterns are drafted for an A cup. If the pattern is drafted for a B cup, then add 2”, etc. Now bring that measurement over to the Size Chart to see where it falls. Let’s say your upper bust measures 40.5”, add 1” to that = 41.5”. Looking at the Sister Faye size chart below, that would put you at a size 16. Your full bust measurement is actually 44”, which is 2.5” larger than the cup size the pattern was drafted for. That means your FBA amount is 2.5”. Still with me?? Let’s kick the confusion up a notch because you need to divide 2.5” by two. Why? We only work on half of the bodice pattern at a time, so we only need half of our full adjustment amount, ie: 1.25”. Remember this amount for later.

Making the Adjustment:

I recommend reading all the way through to the bottom of the page before you begin so you can get a better idea of your options and the order of operations. At the end of the page there is a note about dealing with longer garments, ie dresses.

**Step 1:** Find the bust apex on the pattern. This is usually easier for patterns that have a bust dart, but I have found that bust apex locations can vary greatly so it is always good to include this step. Hold the front pattern piece up to your body, making sure the grainline and center front line is vertical and in the correct position on your body. Mark where the fullest part of your bust is (usually the nipple, but not always).
**Step 2:** Mark the stitch lines on your pattern piece (shown here as a dashed line). Look at what the seam allowance is from your instructions and mark accordingly.

Full Bust Adjustment Slash Lines — **Step 3:** Draw your slash lines.
***Line 1 -*** From the apex to the armscye. This is generally ⅓ of the way up the armscye, it's okay to eyeball it.
***Line 2 -*** From the apex straight down to the hem. This should be parallel to the center front line.
***Line 3 -*** From the apex to the side seam. A good starting point for this line is about 2” below the armhole. If you choose to have a dart, this line will determine its location so make sure you like the look of it
***Line 4 -*** Draw a line perpendicular to Line 2, a few inches up from the hemline. is, the way you tell your story online can make all the difference.

**Step 4:** Slash! Starting at the hem of Line 2, cut to the apex point, pivot and continue cutting Line 1 until you reach the stitch line. You do not want to cut all the way through Line 1 because we need a little hinge to properly do the adjustment.
Now cut from the armscye into the seam allowance, making sure you leave a few millimeters for a hinge.

**Step 5:** Cut Line 3 from the side seam, stopping just before you reach the apex point. Again, we want a small hinge here.

Full bust adjustment dartless block — **Step 6:** Spread! Carefully slide a piece of pattern under your pattern piece. Remember the adjustment amount you calculated earlier? In my example the full adjustment amount is 2.5”, but we only need half of that so we are working with 1.25”. Spread Line 2 so there is a 1.25” gap between the pieces. I find it easiest to tape the center front down and draw a parallel line 1.25” away so you have a nice guideline to work with. It is okay if the pattern is looking wonky and like it has 2 darts, you just want to make sure the center front and both sides of Line 2 are parallel with each other.

Great job for making it this far! Now you get to decide if you want to keep a bust dart or if you want to pivot it to the hem. Keeping the dart is a great way to add shaping to the bust and will not much affect the shape of the hem. Pivoting the bust dart retains the original style of the bodice but will create additional volume at the hem since we will be taking the excess and moving it down. In the end it is a personal preference with overall style and fabric to take into consideration. For dresses without a waist seam I lean toward keep the bust dart as moving it to the hem could greatly alter the angle of the side seam.