Underwires and the Proper Bra Fit

Every woman who wears underwire bras needs to understand underwire sizing. Breasts have a diameter and a projection. When you select a cup size (e.g. B, DD etc.) you are making a breast projection selection.

Each band size has a pre-determined breast diameter built into it in the form of an underwire. Changing your band size can change the underwire diameter. It is also a fact that the same size underwire is used in different cup sizes - the underwire in a 36C is the same underwire used in a 34D and a 38B cup sizes.

Finding Your Underwire Size:

Find your bra size on the chart below. Every bra size in the same diagonal color stripe uses the exact same underwire size.

Now that you understand underwire sizing, here's how you can use this information. Say you've found a bra that fits you great in the cups, but is tight around your ribcage. You now know that when you go up a band size and down a cup size, you will have the same fitting cup diameter (the same wire will be used) but a larger band. This also explains why underwire swimsuits with just a cup size like a "C" don't fit all C cup women. And, for you analytical types who are probably wondering, the diameter increase between standard underwire sizes is approximately 3/8". A standard underwire's length increase between sizes is approximately 5/8".

Underwires are designed to have some spring. Made out of heavy gauge wire, sheet metal or plastic, they splay or spread wider once a bra is put on and fastened. Then they return to their original shape when the bra is taken off. This springing or splay gives additional support to your breasts. If your breasts are wider than the splayed diameter of the underwire, over time the pressure and weight of your breasts can cause an underwire to break in half. Wire breakage can also occur if your band size is too small and thus over-splaying the underwires.

30A	30B	30C	30D	30E	30F	30G	30H	30I
32A	32B	32C	32D	32E	32F	32G	32H	32I
34A	34B	34C	34D	34E	34F	34G	34H	34I
36A	36B	36C	36D	36E	36F	36G	36H	36I
38A	38B	38C	38D	38E	38F	38G	38H	38I
40A	40B	40C	40D	40E	40F	40G	40H	40I
42A	42B	42C	42D	42E	42F	42G	42H	42I
44A	44B	44C	44D	44E	44F	44G	44H	44I

Underwire shapes can vary among brands. In fact, lingerie manufacturers claim their underwire grading and shaping to be the secret behind their unique fit. This is why you may find wire variations among manufacturers. This is also why one manufacturer may fit you better than another. Underwires also have different lengths - though their curve will maintain the same shape. For example, demi cup and low-plunge bra styles will have shorter wires. Underwires in petite bras will also be shorter in length to accommodate a shorter torso. Strapless bras tend to have the longest underwires. Since they do not have the benefit of strap support, strapless bras compensate by having more wire surrounding the breast to give more support.