Breasts come in all shapes and sizes, and you might need to alter your bra pattern to get the best fit. Sometimes the apex position just doesn’t land in the right place, and can cause the breasts to point towards the sides instead of forward. This problem is common among people with a small band and large cup size.
The following tutorial is included in my Maritza Sports Bra pattern, and therefore demonstrates the alterations with a diagonal seam cup, but this method can be applied with other cup styles.
To begin, try on your trial bra and decide where you want to move the apex. If you are having east/west issues, you will probably need the apex to come more towards the center front, and possibly upwards as well.
Remove 1/4”/6mm seam allowance along the cup seam line for both Upper Cup and Lower Cup pieces. Mark the apex positions before trimming off the seam allowance.
On your table, align the Upper Cup and Bridge pieces. It helps to get the Upper Cup in the correct orientation to decide where to make the pattern alteration.
Mark the new apex position on the Upper Cup. On
this example it is raised up and more towards center front.
Draw a new seam from corner to corner going through
the new apex.
Cut apart on the new cup seam, marking the new apex on both pieces.
The length removed from the Upper Cup now needs to be added to the Lower Cup to keep the same cup volume. Flip over the piece cut off from the Upper Cup and align to the Lower Cup at the original apex notches.
Re-draw the Lower Cup, blending into the corners
Check the seam length on both pieces with a measuring tape and note the seam lengths. The lines will not be the same length; the Upper Cup will be shorter than the Lower Cup.
Adjust the curve of the line to make the seam lengths
match. Now a small bit of math:
Subtract the Upper Cup from the Lower Cup. In this
example it is 5.4-4.8= .6.
Divide by 2 to split the difference to adjust each cup.
.6/2= .3
Now divide that by 2 to get the length to adjust each end
of the cup: .3/2= .15.
Adjust the ends of each cup seam .15”, increasing the
length on the Upper Cup and decreasing the length on
the Lower Cup.
In the illustration, the new lines are in black, the original
lines are grey.
Measure again to make sure that the seam
lengths match. Measure the new apex position on
the Upper Cup along the seam line and mark on
the Lower Cup.
Add 1/4”/6mm seam allowance and apex notches to both pieces.