Your rib cage shape can make a big difference to your bra fit. Regardless of your dress size the dimensions of your torso can alter which kinds of bras fit you best. Here is a simple guide to some of the variations in rib cage shape and how they affect bra fit.
This is the most common torso shape and not to be confused with whether your overall figure is straight or curvy. On a straight torso your bra will sit evenly across all the hooks at the back. If you have a straight and narrow torso then look for bras with narrow wires.
If you have a straight and wide torso and your breasts are wide across your body then you probably need bras with wide wires. If you have a wide, straight torso (often referred to as a broad back) and your breasts are close set or narrow then you may need to add inches to your band size and reduce your cup letter.
When your rib cage is dramatically smaller at the underbust than the overbust measurement it can affect the way your bra sits. Lots of women find bras with fewer hooks at the back (2 rather than 3 or 4) sit better. It's quite possible that you need to go up a band size to accommodate the widening of your rib cage across the wider part of your rib cage. A common alteration for flared rib cages is to bend the wires under the armpit away from the body.
Often referred to as barrel chests, this rounding of the ribcage means that you need a lot of band and potentially not a lot of cup so you may need to add inches to your band for comfort. This also works for women with curved spines due to health or posture issues. If you have a narrow and round torso then you will most likely need narrow wires which can accommodate a lot of bust in a small width.
If you have a wide, round torso then you'll need to asses whether your breasts need wide or narrow wires. Again you might need to add inches to the band but this also depends largely on whether you have a squidgy torso. A lot of women with rounded torsos find that they need to bend their wires both around the ribs and away from the sternum so that the wires follow the curvature of their rib cage.
It's important to remember that no one piece of bra information is gospel, so many other factors can affect your fit but this is a general guide to understanding how the shape and contours of your torso can change your bra fit. xx