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How to know if you need an FBA

Creative Counselor: How to know if you need an FBA from pattern measurements

Happy Monday peeps!  I have been buried neck-deep in Archer sewing these last couple of weeks because I decided to finally make sure that I properly fitted the pattern.  And let me tell you, that can take a while!

I am blessed with a body that is pretty “standard.”  It’s not particularly tall or particularly thin, but my proportions are such that I’m pretty close to the standard pattern block and most patterns fit me fairly well straight out of the envelope.  I’m not saying that to make anyone feel jealous, but simply to illustrate that even a mostly-standard body still needs pattern adjustments to get a perfectly fitting garment!

Since I went through time to painstakingly fit this top, I decided that I would document and do tutorials on my fitting changes.  And I did … over at the Sew the Show blog!  I’m hosting an impromptu “Archer week” over there, so you should definitely follow along to see how I make my most common fitting adjustments.

Today I’m over there demonstrating how I did an FBA (full bust adjustment) on the Archer.  Most FBA tutorials work off a pattern with bust darts, but the Archer doesn’t have a bust dart.  That means that those tutorials only work for this pattern up to a point.  Without a bust dart, you have to make some additional modifications to your pattern piece for everything to work out.  I take you through all the steps I followed to get a great FBA on this dartless pattern (tutorial is here).

But how do I know if I need an FBA, you might ask?

Good question!  There’s always the trial and error method.  Make a muslin of the pattern as drafted and see where the pulls and wrinkles are.  If there’s lots of pulling around the arm and bust area, or if the fabric is struggling to easily cover your boobs, you might need an FBA.

Ugh, I hate making muslins…

Me too sista (or brotha)!  Though muslins are a fact of life for a sewist who wants his or her clothes to fit properly, they still suck and I try to make as few of them as possible.

Not too long ago, I realized a trick to know pretty accurately whether I was going to need an FBA on any given pattern without making a muslin (and it works for an SBA — small bust adjustment — too).

Creative Counselor: How to know if you need an FBA from pattern measurements

To figure out whether you need an FBA or SBA on a pattern there are a couple of things you need to know.

1. Determine the cup size that the sewing pattern is drafted for.

You may be asking, “How the heck am I supposed to know that?”  And that’s also a fair question since most pattern designers don’t typically include this information in their patterns, though they really, REALLY should.  Cup size has a huge impact on how a particular pattern will fit — in my opinion it’s a key piece of information to have on any pattern.

But, where to find it.  Well, my Sew the Show partner-in-crime Becca did a lot of that work for us!  A while back she surveyed an impressive number of indie pattern designers and got them to spill their guts about cup size.  When I need to know the cup size on a pattern, my first stop is here, where Becca has compiled information, including cup size, for most of the major indie pattern companies.

If the designer whose pattern you’re sewing isn’t on the chart, my next option would be to email the designer and ask.  I find most indie designers to be approachable and responsive, so they’d probably tell you the cup size on their block.  If it’s a Big 4, it’s going to be a B cup, since that’s “industry standard” for pattern design.

If the designer isn’t on Becca’s list, and doesn’t respond to your email (or it’s 9pm and you want to work on it that night), you can calculate the cup size of the pattern by taking 2 measurements from the pattern pieces

  1. Upper bust, and
  2. Full bust.

Subtract the upper bust measurement from the full bust.  If the difference is 1″, then it’s an A cup.  Two inches for a B cup, 3 for a C cup, and so on.  Most patterns are going to be either a B or C cup.

Once you know the cup size of the pattern,

2.  Determine your own cup size.

Remember how we just calculated the cup size of the pattern based on upper and full bust measurements?

You got it — do the same thing for yourself!

Take (or even better, have a friend take) your full bust measurement around the fullest part of your chest.  Then take your upper bust measurement above the breasts and around to the bra fastening in the back.

Subtract the upper bust measurement from the full bust to get your cup size.

  • 1″ difference = A cup
  • 2″ difference = B cup
  • 3″ difference = C cup
  • 4″ difference = D cup
  • 5″ difference = E cup (or DD)

And so on.

If your cup size differs from the pattern’s cup size, chances are you’ll need to adjust the bust, either with an FBA or an SBA.

In my case, I was working with the Grainline Archer, and Becca’s handy-dandy chart shows me that Grainline drafts for a B cup.  My upper bust measurement is 32″ and my full bust measurement is 35″, making me a C cup. Chances were pretty good that I was going to need an FBA.

But how much of an FBA?  And how do I choose my size?

That’s actually a pretty easy answer, and just requires some basic math.

3.  Convert your cup size to the pattern’s cup size based on your upper bust measurement.

Now that you know your upper bust measurement, you can figure out which pattern size corresponds with that measurement.

To figure that out, take your upper bust measurement and add the corresponding number of inches for the pattern’s bust size.

In my case, my upper bust measurement is 32″ and Grainline drafts for a B cup.  So by adding 2″ (for a B cup) to my 32″ upper bust measurement, I know that the size 4, with its 34″ full bust measurement, is the size that best correspondence to my shoulders.

4.  Calculate your FBA.

After hearkening back to elementary school math, I know that a size 4 will be the best fit for my shoulders.  But I also know that the size 4 is drafted for a 34″ full bust and my full bust is 35″.  That means I need to add an extra inch through my FBA.

And that’s really it!  A few basic pieces of information, some simple addition and subtractions, and you can know with a decent level of certainty whether you need a bust adjustment to get a great fitting garment.

The bust adjustment is usually the first and most basic adjustment on any garment.  Everything else flows from the bust adjustment.  I ended up with a great-fitting Archer shirt, and my FBA was the first step in the process.  I’ll detail the whole process over at Sew the Show this week!

0 thoughts on “How to know if you need an FBA

  1. This is very helpful information! I have a question – what if my bust measurement is 1″ smaller than what the pattern says? I could take out 1/2″ but is it worth it? I usually don’t do a SBA, and I don’t know a lot about doing them.

    1. Hmmm, whether you can get away without the SBA probably depends to a certain extent on the pattern. If it’s a pattern that’s meant to fit loose and baggy, you probably can get away with it. But 1″ is enough that it’s probably pushing you from one size to the next if you go by your full bust measurement alone.

      The main thing that the calculations I do tells me is what size will fit my shoulders and then what I need to do to make the bust fit well from there. In my case, since my cup size is bigger than the pattern, the size that corresponds with my full bust measurement is too big in the shoulders. In your case, since your cup size is smaller than the pattern, the size that corresponds with your full bust measurement is going to be too small in the shoulders. I needed to size down with an FBA and you need to size up with an SBA.

      So regardless of whether you choose to do the SBA, I’d say that you should choose your size based on the pattern size calculated from your upper bust measurement. So in the Archer example, if I was an A cup instead of a C cup, my full bust measurement would put me in a size 2. But since my upper bust measurement is 32″, that size 2 is going to be too tight in the shoulders. I would need to take my 32″ upper bust measurement, add 2″ for a B cup and then cut a size 4 to fit my shoulders. You should probably use a similar method to choose your size to make sure that your garment isn’t tight in the shoulders.

      From there, whether you make the SBA is really a matter of preference, I guess. I think you would notice a difference in the fit and the adjustment is easy to make. I think I’ll try to do a similar SBA tutorial, but until then, the Colette blog has a pretty good one here:

  2. Thanks for this info! Are the cup sizes that patterns are designed for always based on the difference between the full bust and the HIGH bust? in that case, i would be a b/c but i am most definitely that in my bra size!

    1. Yes, that is how sewing cup size is determined, which can be different from bra cup size. Bra size is frequently measured using the under bust measurement, rather than the over bust measurement, so it can be different than sewing cup, particularly on someone who has wide or narrow shoulders.

  3. This probably seems silly, but most of the indie patterns I own don’t have an upper bust measurement. Where should that be taken on the pattern, if it’s not given?

    1. Yeah, unfortunately most patterns don’t list this information, even though it is incredibly important! If the designer isn’t listed on Becca’s list, then you would probably measure from right under the armpit to just under the neckline on the front piece and straight across the back at the bra line. And then double it of course if the pieces are on the fold.

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