Our new 4th Ed. Irish dance solo dress pattern is coming out soon with a Bust Cup Adjustment add-on! Our fashion line also includes these options, but we’re thrilled to be able to offer this feature in our Irish dance patterns too! I thought this was a great time to talk about why cup adjustments are amazing, how different cup sizes influence the fit of the pattern, and how to determine your own bust cup size.
What are Pattern Bust Cups?
While pattern cup sizes use the same A, B, C, D, DD, etc classifications as bras, they are based upon different measurements. Bra cups are measured as the difference between the circumference of the full bust and the circumference of the ribcage right below the breasts. This makes sense, because we want a good-fitting anchor around our ribcage, and cups that will extend the proper distance out from that to perfectly hug our boobs. Pattern cup sizes on the other hand, are based on the difference between the full bust and the ribcage ABOVE it. It’s common for your bra cup and pattern cup to be different.
How do they influence the fit of the garment?
Most commercial patterns are drafted with a pattern B-cup, which assumes a 2-inch difference between those measurements. If the company doesn’t give any information on this in their sizing, you can usually assume it’s a B. When using a pattern, we choose our size based on our full bust measurement, but flat- or full-chested folks will tell you that this doesn’t mean you’re guaranteed a good fit.
Imagine you get a breast-reduction or -addition procedure. Your full bust measurement will change, but your ribcage and skeleton will remain the same. This is what we are changing when we adjust the bust cup size of our pattern. In the image to the left, we see four patterns, all size 6, with A- (pink), B- (orange), C- (green), and D- (blue) cups. As the cup increases, we see the bust widen, but the shoulders and waist remain the same width. We also see the pattern lengthen, since it will be a slightly longer distance over a large bust than a small one.
Let’s compare that to two patterns that have the same full bust measurement. To the right, we have a size 6 with a D cup (blue, 37 inch bust), and a size 10 with an A cup (pink, also 37 inch bust). In the A-cup (pink), the bust width is pretty evenly split between the back and front, but in the D-cup (blue), more if it has been shifted towards the front. The D-cup also has a smaller shoulder. If we picture the wearers of these two patterns, the A-cup wearer will have a bigger frame (skeleton, shoulders, ribcage, etc) than the D-cup wearer. If both were to wear regular B-cup garments based off their bust measurement, the A-cup’s dress would be tight in the shoulders and armhole. The D-cup’s dress on the other hand would have a lot of excess in the shoulder with gaping armholes.
How to determine your own cup size
Wear thin clothing, and a normal, lightly padded bra (or the type of bra you expect to wear with the garment you’re measuring for). Stand up straight with ears, shoulders, hips, and feet in alignment. Always have a second person do the measuring, as this will yield much more accurate results than attempting to take your own measurements.
Full Bust: wrap the tape measure around the largest part of the bust, level with the floor. Don’t pull the tape measure too snugly, or you will underestimate the measurement.
High Chest: wrap the tape measure around the upper chest; under the arms but above the main part of the breast. Pull the tape measure snugly. It may not be parallel with the floor.
A 2-inch difference in the High Chest and Full Bust measurements is considered a “pattern B-cup” (a difference of 1″ = A-cup, 3″ = C-cup, 4″ = D-cup, 5”=DD-cup, etc). Round to the closest whole number, or round up if exactly half-way in-between.
Choose your bust size based on the High Chest measurement, and your cup based off your Full Bust measurement.
Adjust existing patterns using a Full Bust or Small Bust Adjustment
Using a pattern with cup adjustments is all fine and good, but what about if you need to change the cup size of an existing pattern? The Full Bust Adjustment (to increase the cup size) is fairly well known, but as a flat-chested person I’d like to give a shout-out to the Small Bust Adjustment (to decrease cup size) too! Both alterations change the width of the bust without changing the shoulders, armhole, or waist. We offer guidance on these alterations and much more in our guide “Pattern Alterations for Better Fit”, which can be found here.