Sewing Bust Adjustments 101
One of the best things about sewing is the ability to create clothing perfectly made to fit your own unique and beautiful body. You shouldn’t have to try to make yourself fit clothes- the clothes should be made to fit YOU! A very common adjustment that often has to be made for a perfect fit in adult clothing is a bust adjustment. In this miniseries we will be looking at how and when to do bust adjustments, including the Full Bust Adjustment, commonly known as an FBA, and small bust adjustment, or SBA.
Let’s answer some common bust adjustment questions!
What is a bust adjustment?
In sewing, we measure the bust in two or more places. The most common, and most important to fit, are the upper bust and full bust. You can also measure the under bust. This is especially important when sewing undergarments and close fitting woven garments. For the bust adjustment purposes, we will be looking at only the upper bust and full bust.
A bust adjustment is done to make the bust area of the bodice of a pattern larger or smaller than the base size of the bodice. This distributes the fabric to the correct places on the body, adding or reducing the amount of fabric in the fullest part of the chest without making the bodice smaller or larger anywhere else. This ensures a perfect fit!
What is the upper bust? What is the full bust?
Both measurements are girth measurements: they are measured around the body. The upper bust measurement is taken around the body just below the armpits, above the full bust. The full bust measurement is taken around the body at the apex (fullest) part of the bust. These measurements should be taken freshly for each new pattern you sew, wearing the undergarments you plan to wear with the finished garment you are sewing.
What is a cup size in sewing?
In sewing, cup size refers to the difference between upper bust and full bust measurement. In Boo and Lu patterns, you are instructed to choose bodice using your upper bust size. You then choose your cup size by comparing the measurements between upper and full bust. The difference between the two measurements tells you your cup size.
A pattern that does not come with cup size options is often drafted for a B cup. At Boo and Lu, most adult patterns that were released May 2024 and later have cup size options. Any that do not were drafted with a B cup as the base. A B cup means that the full bust measurement is 2″ larger than the upper bust measurement.
Example
In the Boo and Lu adult size chart, a size 10 has a 37″ upper bust. Any model with a 37″ upper bust would begin with a size 10 bodice. But which cup size?
- 37″ upper bust with 38″ full bust: size 10, A cup
- 37″ upper bust with 39″ full bust: size 10, B cup
- 37″ upper bust with 40″ full bust: size 10, C cup
- 37″ upper bust with 41″ full bust: size 10, D cup
- etc.
A bust adjustment is needed if the cup size is smaller or larger than what the pattern is drafted for.
Any cup size different than a B cup will need an adjustment if the pattern is only drafted for a B cup.
Note: Some Boo and Lu patterns do not have cup sizes because they are drafted with enough ease that simple blending/grading is all that is needed for a great fit. The individual pattern tutorial will give the instruction on this!
If a pattern is drafted for cup sizes A-D, a Small Bust Adjustment (SBA) is necessary if the cup size is smaller than an A cup. This is when the full bust measurement is the same as the upper bust measurement, OR if the upper bust is larger than the full bust.
If a pattern is drafted for cup sizes A-D, a Full Bust Adjustment (FBA) is necessary if the cup size is larger than a D cup. This is when the full bust measures 5″ or more larger than the upper bust.
How do I know how much to adjust?
The answer is in the measurements!
For every ONE INCH difference between the upper bust and full bust measurement that is DIFFERENT than the base cup size, you will add/subtract HALF INCH.
What does that mean? Let’s look at some examples!
On a pattern drafted with only a B cup bodice base:
37″ upper bust, 40″ full bust. This model is a C cup because there is a three inch difference between the upper and full bust measurement. A B cup is a 2″ difference. This means that this model has a bust 1″ bigger than a B cup. The adjustment will be to add 1/2″ in an FBA.
37″ upper bust, 42″ full bust. This model is a DD cup because there is a five inch difference between the upper and full bust measurement. A B cup is a 2″ difference. This means that this model has a bust 3″ bigger than a B cup. The adjustment will be to add 1.5″ in an FBA.
37″ upper bust, 38″ full bust. This model is an A cup because there is a one inch difference between the upper and full bust measurement. A B cup is a 2″ difference. This means that this model has a bust 1″ smaller than a B cup. The adjustment will be to subtract 1/2″ in an SBA.
On a pattern drafted with cups A-D bodice base:
37″ upper bust, 42″ full bust. This model is a DD cup because there is a five inch difference between the upper and full bust measurement. A D cup is a 4″ difference. This means that this model has a bust 1″ bigger than a D cup. The adjustment will be to BEGIN with the D cup bodice pattern piece, then ADD 1/2″ using an FBA.
37″ upper bust, 37″ full bust. This model is an AA cup because the upper bust and full bust are the same, there is a 0″ difference. An A cup is a 1″ difference. This means that this model has a bust 1″ smaller than an A cup. The adjustment will be to BEGIN with the A cup bodice pattern piece, then SUBTRACT 1/2″ using an SBA.
SBA, FBA…. How do I do these??
Now that you understand if you need a bust adjustment, and how much, all you need to do is make the adjustments! I promise, it is easier than it sounds. In the rest of this series, we are tackling the elusive SBA and FBA, and with some practice, you are going to walk away CONFIDENT in your ability to make the adjustments.
Bust adjustments make a world of difference to the fit of a garment. If you need an FBA, you need to add fabric to the fullest part of the bust, without making the entire garment bigger. You don’t need the shoulders and back and waist to become baggy! You just want the added fabric where you need it. If you need an SBA, you need less fabric at the fullest part of the bust, but you don’t want it tight all over!
Learning to make bust adjustments can seem intimidating at first, but it is a skill that you will love having. Wearing custom clothing perfectly tailored to your unique body is one of the best things about sewing, and learning to alter patterns to YOUR shape is well worth the time and effort.
Complete List of Posts in the Bust Adjustment Series
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Happy Sewing!
