Scroop Patterns

The Ngaio Blouse – the difference in cup sizes, illustrated

The Scroop Ngaio Blouse

When I first planned the Ngaio Blouse as a pattern I intended to offer it in one standard size, and do a tutorial on how to do a full bust adjustment (FBA) on it, since the pattern pieces aren’t standard shapes that most sewers are used to adjusting. Then I thought: why not just do it for you?

The Scroop Ngaio Blouse

I thought you might appreciate a bit of insight into the method I used, the calculations behind it, and what affect that has on the final fit.

The simplest way to measure cup size is to measure the difference between your full bust measure, and your high bust measure:

The Scroop Ngaio Blouse

According to this system, an A cup has a 1″ difference, a B cup has a 2″ difference, a C cup a 3″, etc, etc.

This is the measuring system I use for the Ngaio blouse, because it works reasonably well for most bodies, is the same system most other pattern companies use (so I’m not throwing a bunch of weird measures you’re not expecting at you), and is simple to measure and calculate.  However, it isn’t a perfect system by any means, because it  doesn’t  take into account:

Ribcage shape:  If you have a very square/rectangular ribcage, or a very triangular ribcage, the same size pattern will fit you differently,  For example, Ms. T and Ms R have the exact same high and full bust measure, but Ms T has a very triangular ribcage, and Ms R has a square/rectangular ribcage, so their underbust measures are 4″ different.  For her bra to fit properly, Ms T  is almost certainly going to wear a bra that is significantly smaller in the band width, and significantly bigger in the cup size, than Ms R.

Breast shape: The overbust vs full bust measure system assumes that breasts stick out from the body proportionately to increases in cup size, but that isn’t how many busts work.  Breasts  can be small, but very pointy, or large, but flatter  and more spreading.

Because of these imperfections in the measuring system, the cup size you get when  calculating your bust size for the Ngaio blouse may not match the cup size you’re used to wearing in a bra.  That’s OK!  Just follow the pattern, but make a toile (as is recommended with every pattern)  to check the fit and make adjustments.

If you’re between measures according to the system you should think about your back and shoulders.  If you have a narrow back and small shoulders, you’re probably going to fit better in the larger cup size that you’re between, which will put you in an overall smaller size.  If you have a wide back and wide shoulders, you’ll probably fit better in an overall larger size, with a smaller cup size.

To show the difference in cup sizing, the gorgeous  Jenni (who sits best in the Large cup sizing) modelled both Ngaio in both the Medium and the Large cup sizing.

Here is Jenni in her size, but with a Medium cup:

The Scroop Ngaio Blouse

The Scroop Ngaio Blouse

The Scroop Ngaio Blouse

Note how the bust line sits on her bust, instead of under it, and how the top wants to crease and pull from back to front, and all the extra fullness below the bust.

Now, in the correct bust size according to her measures:

The Scroop Ngaio Blouse

The Scroop Ngaio Blouse

The Scroop Ngaio Blouse

The bust line sits under her bust, and the blouse sits smoothly below the bust, skimming the stomach,  with no pulling and wrinkles from back to front.

Of course, different cup sizing still doesn’t  take into account how high or low your bust sits on your body, which takes its own adjustment.


  1. Elise says

    My pet peeve is seeing seam go across busts, rather than under them. Very cool to craft a blouse that takes bust size into account, not just waist size.

  2. Jo says

    Am I the only one who thinks the first blouse looks great fitted like that, as a casual-yet-cutely-detailed tuck-in blouse? Great patterns you’ve got here . . . starting to be very tempting . . .

  3. Natalie says

    I truly love this! And finally understand how bust alterations work. The blouse is truly gorgeous also.

    However, I wear a 12DD bra, and my high bust is slightly larger than my full bust. Which bust size would I choose?

    • Hmmm…that is a conundrum! Larger high busts than full is something I encounter in less than 1 in 100 of my sewing students. I’m guessing you’re pretty wide across the back? I’d start with a toile at the Medium, and see how that goes. I’m happy to help sort out Fitssues if needed!

      • Depending on the size difference you may be able to use a different size back from front. I have the opposite problem – I usually need a 14 across the back, but an 18 or even 20 across the front in addition to a full bust change for H cup UK (K cup US+/-). Really the whole thing is a pain in the neck.

  4. Karen says

    Thank you – this is so helpful! You always put a little something extra into pattern development. 🙂

  5. Lorna says

    I love this pattern! I’m on the short side, so I took 1/2 inch off the top, shortening the neckline, upper back and sleeves. The cup size variations really made this perfect.

    So far I’ve made 2 – a light fabric more dressy one and a cotton everyday top.

    So quick to make up, I made both in one day. And! no buttons or zippers. Just slip-on goodness. Next I’m going to try a summer dress version by hacking on a skirt.

    Thank you for this pattern!

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