Bra Tips: Fitting An Underwire

Finding Your Wire Size | Cloth Habit

It’s reader question day! Recently, a reader asked by email: How do you know what size to start with? The wires in my bras dig into the breast tissue under my arm and it’s so uncomfortable!

I can definitely relate to that! I’ve written about wires & fitting a few times, but today I’ll share a bit more for the first-time bra-makers or for those who’ve been having a hard time figuring out where to start!

When I bought my first bra-making kit, I was very confused about wire sizes. Weren’t they all the same? It wasn’t until I started pulling out wires from old bras and fitting others that I realized how different they can be. Wires come in many shapes, sizing gaps and strengths. For example, these are both full length wires for a 32F bra:

Finding Your Wire Size | Cloth Habit

I pulled the narrower one from a Panache bra, and the white one is from my collection. The reason I share this is so you can see that wire sizes aren’t a static thing. So the very best way to start is buying a few wires and trying them on–without worrying about what size you are. Try a set of wires in the size you think you are (or are currently wearing), and then a size up or down. Or if your wires typically feel tight, you could try the next two sizes up.

When trying on the wire, place it up against your breast root, the area where your breast tissue joins your chest wall. It should rest comfortably against the edges of your breast like it is sitting in a pocket. If you’re having trouble seeing your breast root, lift your breast tissue up higher or even raise your arms to see this line.

Finding Your Wire Size | Cloth Habit

Finding the root on the side of your breast can sometimes be a little harder. Some of us have breast tissue under the arms. And sometimes it is hard to see where extra fatty tissue from our arms or side is distinct from breast tissue. (There are a lot of opinions about whether or not underarm flesh is “migrated” breast tissue, but this is something I’d rather hear from my OBGYN. Please ask yours if you have questions about it.) In this case, try to find the wire that sits most comfortably against the side of your breast and doesn’t look like it is riding up onto your actual breast.

Hopefully this will give you a good place to start. Unless you have the special opportunity of taking a bra-fitting workshop in person, you will have to buy and try a few until you find one you like, which I believe is worth the small investment!

special cases

Sometimes there are special cases in wire fitting. Perhaps you have made a bra or two and still feel like something is wrong in your wire fit. So let’s discuss a few of those!

1. Pokey Wires

Perhaps the wire that seems to fit may seem a little too long or too pokey for your comfort. This might be the case if your breasts are higher up on your chest, closer to your underarms. Instead of trying to hunt down a shorter wire, consider buying some wire cutters! They’re an inexpensive investment and my bra-making friend–I wrote about cutting and tipping wires in this post.

2. Big Cup, Small Band

Traditionally, wire sizes increase by anywhere from 6 to 10mm in diameter per size. And as the sizes go up, these varying “grading” increases can add up to big differences for larger cups. If you have the cup volume of a 36D but have a small ribcage, the traditional wire for that size might have too wide of a diameter and could possibly wrap too far into your side.

In this case, you may want to look for a wire that is long enough to encase your breast but narrower in diameter. The Panache wire in my earlier photo is a narrower wire. Both Bra-makers Supply and Sewing Chest UK sell narrow but long wires.

3. Small Cup Needs

The opposite is true for some women who have small cups but an average band. You may have the breast volume of a 34A but need the wire with the width of a 34B. This is my personal issue. I wear a 30D bra with a wire one size larger–and cut the side length down so it doesn’t cut into my underarm.

(Please take note: I’m not an expert on special medical conditions. These are just the common issues that I have encountered.)

I hope this helps you in the search for wires! Just remember, how a wire fits and feels is a very personal thing. And even a small change in weight, post-breast feeding, etc., can change your wire size and comfort. Only you will really know how it feels, and whether you actually want to wear one! So don’t be afraid to experiment.


  1. Ginny says:

    Hi Amy :D! You may have posted this video during last year’s bra-making sewalong, but honestly I cannot recall if that is where I first saw it. I’ve found this method very helpful when trying to determine underwire size for friends and relatives. It helps me hone in on where to begin size-wise anyway.

    • Amy says:

      Hi Ginny, thanks for sharing. I do remember this video. There is also another way to do this with a flexible ruler–scroll down this page for the section on “breast root trace”.

      I’ve tried both and have a really really hard time not bending the wire/ruler out of shape as I pull it away. It is easier for me to just bring some wires to a fitting and try a series of them on, but others may have more success with those methods!

  2. Gwenan says:

    Hi, this is interesting thanks! I want to get into making my own bras but I think it’ll take me a while to get there (not the fastest sewer and have a queue of other things I’m desperate to make!) In the meantime, I’m wondering if it’s worth trying to change the wires in my RTW bras to longer ones… I have some that are *almost* really comfortable and seem like a good fit generally, but the ends of the wires squeeze inwards, which gets uncomfortable… have you ever tried this? Do you think it would work if the change isn’t too drastic? I’m guessing you couldn’t go more than a few mm wider without distorting the shape of the bra too much…

    • Amy says:

      Hi Gwenan, a few people have asked me about this. It is possible to change wires in your bras. You want to find a way to get the channeling open. That either requires 1. unstitching the elastic and the bartacking that closes the channeling at the underarm or 2. cutting a slit in the channeling and then using something like moleskin to patch it up afterward. I have done the first–which was a real pain!–but not the second. It sounds like your wires may be either too narrow or have a steep curve at the side. You could also try cutting the wire down at the side just a little bit and seeing if that makes it more comfortable.

      Hope that helps! ♥Amy

  3. Laura says:

    You’re a mind reader!

    I’ve just bought a kit ready for my first attempt at bra making, but I have no idea where to start with the underwires. This is so helpful – thanks!

  4. Sophie-Lee says:

    Another thing to keep in mind (I learned the hard way after recently making my first bra) – it’s easy to have the right underwire but you’ll need to adjust the actual pattern. I had my underwire right but sewed the “base” of the cup too small/narrow, so the underwire got pulled in to lay on my lateral breast tissue

    • Amy says:

      Hi Sophie! Yes that can happen. Adjusting the cup, or even going up or down a cup size, is something almost everyone has to do because we are all different shapes. Fitting the underwire is the first step I do, because it has the most impact on the fit.

      • Robin says:

        Is there an easy way to know if you need to modify the wire edge pieces of a pattern to accommodate different wire sizes? Will someone making, for example, a bra with a size 38 wire be able to keep their pattern the same as someone making the same bra size but with a 48 wire, or vice versa?My underwire size is four sizes larger than the ones used in RTW bras that are my size and otherwise fit, so really I’m curious if I’ll have to modify, and if so is it just a trial and error sort of thing, or is there a standard fix. (First bra, and feeling a little overwhelmed…)

      • Amy says:

        Hi Robin,

        I make these adjustments often. If you are using a different wire than the one the patternmaker used for a certain size, then you will have to make modifications. In drafting bras, cup pieces of a certain size are made to fit a wire/cradle of a certain size and length. To use a different volume cup, I first find a cradle pattern that matches the wire length I want to use. Since you want to use a wire four sizes larger, I would definitely go this route. Find a cradle pattern that matches the wire you want, even if it’s a different size than your cup. Then choose the cup you want to use. In order to keep the same volume, you’ll need to adjust the wire line of the cup pattern so that it is longer and will fit into the new wire.

        In this post I measure wire length to make sure the cradle matches the wire: I also wrote a guest post for Closet Case Files, in which I show an example of how to adjust a smaller cup for a larger/longer wire (and vice versa):

        Hopefully those give you some good ideas on how to adjust your pattern. It will take some trial and error at the beginning—that’s the nature of bra making. Jump in and don’t be afraid to make mistakes! But once you have a cradle and band that fits with a wire, you can use it over and over without needing to start over with every new pattern. I use the same cradle and wire for all my wired bras, regardless of what style or pattern I’m sewing, and make little tweaks from there.

  5. Becky Miller says:

    You are reading my mind. I’ve been fussing with this issue and hesitating on making my next bra because wires have been a mystery to me. Thank you!

  6. Geo P says:

    I had the exact same question as the reader who sent the email! I was going to dig into your first posts from the sew along, but this is perfect, thank you very much!

  7. wahyu says:

    hi, miss amy. im from indonesian. i very like design bra in your websites. if you want share, i need e-book PDF formating how to making bra with pattern. thankyou miss amy. i like your design

  8. Georgia Franchetti says:

    Thanks, this is super helpful. I am starting to draft a bra pattern and was conflicted because my 32DD nursing bras still feel great, but now that I’m not nursing I’m no longer filling the cups. I’ve been wearing a 32D and wondering if the smaller wires are correct or not. I’ve also been wondering if slightly narrower wires would help pull the breast forward- like maybe I should go with a narrower wire for better lift. I think after reading this I’ll try a 38 after all.

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