Why it matters
An underwire should sit in the crease where breast meets ribcage, all the way round, with breast tissue inside it and rib beneath it. If the wire is wider than your root, its ends reach into the armpit. If it is narrower, it sits on breast tissue. Neither can be fixed by changing cup size alone, because wire width and cup volume are tied together within any one style.
Root width
Find yours
Stand upright without a bra. With a fingertip, follow the crease under your breast outward until the soft tissue ends and you feel only ribcage.
- Narrow: it ends on the front of your body.
- Average: it ends about at the front of the armpit.
- Wide: it continues round to your side.
What to wear
| Root | Typical problem | Look for |
|---|---|---|
| Narrow | Wires poke the armpit, empty space at the outer cup | Narrow, U-shaped wires. Plunge styles. Brands cut for projected shapes. |
| Wide | Wires sit on tissue at the side | Wide, open wires. Balconettes, half-cups and many moulded bras. Side-support styles. |
Width tends to go with projection. Narrow roots often come with projected breasts, and wide roots with shallow ones, since the same volume has to go somewhere. See shallow vs projected breasts.
Root height
Find yours
Look at where your breast begins at the top. Lifting the breast gently makes the upper edge easier to see.
- Tall: the breast starts high on the chest, not far below the collarbone, and the tissue reaches up towards the armpit at the side.
- Short: the upper chest is flat and the breast starts lower down.
What to wear
| Root | Typical problem | Look for |
|---|---|---|
| Tall | Low-sided cups cut in at the side and let tissue escape near the arm | Fuller-coverage cups, higher wire tips and side panels |
| Short | High cups and tall wires dig in under the arm, upper cup gapes | Demi, half-cup and plunge styles with low sides |
Root and torso length
How much room you have between the breast crease and the armpit matters as much as the root itself. If you are short in the body, even a wire of the right width may come up too high. Lower-cut styles solve it. See underwire poking your armpit.
Checking a wire on your body
- Put the bra on and scoop and swoop.
- Press along the wire from the centre to its outer end. You should feel rib under it the whole way.
- Look at the outer end. It should finish just behind the breast tissue, pointing roughly at the middle of your armpit.
- Lower your arm. The wire tip should not press into it.
If the wire fails these in every size you try within a style, the style's wire is the wrong shape for your root. Change the style, not the size.
Frequently asked questions
What is the breast root?
The outline where the breast joins the chest wall. Fitters describe it by width, meaning how far round the body it reaches, and by height, meaning how high up the chest it starts.
How do I know if I have a narrow root?
Your breast tissue ends at the front of your body, before your side. In bras, wires tend to extend past the edge of your breast and poke you under the arm, and there is empty cup at the outer edge.
How do I know if I have a wide root?
Your breast tissue continues to your side or towards your armpit. In bras, wires tend to sit on breast tissue at the side even when the cup volume is right.
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