Your breast root refers to the size and shape of the area where your breasts attach to your body. Just to clarify, this isn't to do with the shape of your breasts, which may be shallow, or full or long etc. It's a part of bra fitting that helps you work out which cup wires work for you. There are two measurements to consider when talking about breast roots; your breast root width and your breast root height.
Assessing Your Wire Width
There are, broadly speaking, three breast root widths; average, narrow and wide. The width of your breast root is linked to which width, or shape, of bra wire will work best with your breasts. Your bra wire must never rest on your breast tissue and ideally you don't want it to run very wide of the outside of your breasts (although some gap between your breast root and the bra wire is not terribly detrimental to your fit).
Think of the bottom of your breast root (the area of your breast that attaches to your body underneath your breast) as a smile. You can have a broad, flat smile or you can have a deep, curved smile and you want a bra that has a matching shape to your breast root. By understanding the width of your breast root you can diagnose if a bra wire is too wide or narrow for you when you put it on.
If your bra wire rests on your breast tissue then your first step is to check that your cup volume is large enough. Try a larger cup first and if that doesn't work then the wire shape could be too narrow for the width of your breast root so this isn't a style for you.
If your bra wire goes a long way past your breast root (most commonly this is when there is lots of empty cup around the side of your body, under your armpit) then you can try a cup volume smaller but it's most likely that the wires of the cup are too wide for you and this isn't the bra for you.
Breast Root Height
On average full bust women find that their breast root is between 5 and 7 inches lower than their armpit. If the distance between your breast root base and your armpit is less than 5 inches you often find that bra wires poke into your armpit. If this is the case for you then you have high set breasts and will benefit from bras with short wires that don't rise as high into your armpit.
Fit Point: If you find that you often get empty cup at the bottom of your bra then it could be because your wires are too long for your high set breasts. Look for bras with shorter wires.
If your breast root is farther down your body than 7 inches you can experience spilling at the sides of your bra no matter which size you try. You need tall bras with long wires that run equal to (or higher than) the side of your breasts.
Help Finding the Right Wire
Bratabase is a fantastic resource for finding out whether a bra has long or short wires and how other women have found the fit based on their own breast root width and height.
At Butterfly Collection we include the side height of each bra (the side compromises of the wing and wire) on the product page to help you work out whether the length of the wire is right for your breast root height.
I hope this helps you work out if your bra fit frustrations are being caused by a mismatch between your breast root and wire xx