What follows is based on close to five decades of buying lingerie and includes a bunch of learning thanks to having made every mistake in the book. Some of them more than once.
My first post about bras was about getting the band size right - an art on its own - but if you don't have breasts, then you will need to use forms of one kind or another to fill the cups. One thing worth keeping at the back of your mind is that most bras are not designed for forms, so there are some dos and don'ts worth knowing before you buy.
Anatomy of a bra
Bras are small miracles of design built to support the cups, which are connected by a small flat triangular area at the front, known as the gore. Remember the gore, because it is crucial for fit.
Many bras have an wire that underpins the lower half of the cups – these are metal and liable to expand, which is why you should never wash a bra in hot water. If you do, the wires can expand, poke through the material and gouge holes in things. Painful, or expensive, depending on whether the hole is in you, or one of your precious forms.
Other bras have what are known as 'soft cups' and lack the wire. These are usually, but not exclusively for smaller cup sizes.
Lateral to the cups, forming the inner section of the strap, is a part called the cradle, to which the wing of the strap (that's the stretchy part carrying the hooks) is attached via a vertical seam. In larger cup sizes this seam is usually stiffened with what is called a bone. Why?
Because they used to be made of whalebone. Truly.
The radius of wires is dependent on back size, not cup size – which means a 36D bra has a wider radius wire than a 34D bra, while a 36B shares the same radius of wire with a 36E. This has implications for fitting breast forms.
Until you get to really large cup sizes – where the light engineering principles of corsetry come into play – the band, wire, cradle and wing will be more or less identical between two bras from the same range that are made for the same back size, even if one is a B and the other a D.
So far, I haven't mentioned the straps, which are mostly there to stop the cups falling down. If you read my previous post, bras are designed so the weight of the contents of the cups should fall on the band, not on the straps.
Straps are adjustable, but for some wild reason bras are usually sold with the adjusters set far too short for most backs. If you find yourself pulling the adjuster all the way down to the bottom every time you buy a new bra, you aren't a freak, it's part of the ceremony of bra unboxing.
The part of the cup where it attaches to the strap is called the apex. The positioning of this - relative to a line drawn vertically up from the gore - varies depending on the kind of bra. Learn to notice where it is lies because it will help choosing bras that work for you.
In demi cup bras, the apex may be so far away from the centreline of the gore as to be vertically above the outside end of the wire, while in full cup bras the apex will be nearer the middle. In some bras, for instance Lejaby's Amazone range, it will directly be over the middle of the cup (for which reason the Amazone would be a perfect ordinary wear bra for forms if only the cups didn't follow a cup scale all of their own.)
How cup sizes work
Returning to cup size, the only difference between a 36B and a 36D bra from the same range and style is the depth or fullness of the cups. The wires will have the same radius, the band will be the same length, and everything else about the two bras will match up. So, if you use a pair of forms suitable for the B cup with the D cup bra, the cup material will be slack around the form.
Something else worth knowing – which I will cover in another post – is that the reason wire diameter varies by back size and not by cup size is that the base of the breasts of a woman who takes a 36D are the same width as those of one who wears a 36B. Put another way, the woman wearing the D cup has more volume in her breasts, but because they are no wider than her friend with smaller breasts, this makes them project more.
Breast forms and bras
That may be how anatomy works, but unfortunately, it isn't how breast forms work and instead, suppliers scale both the width and depth of forms with increasing volume. Which means each size of form is a perfect fit for a particular cup and back size and a compromise for all others. This is something the makers of forms – even clinical suppliers – do not make particularly explicit and even surgical fitters can be unaware of it. While it is maddening, it keeps the product ranges simple and cuts cost to both supplier and user, but with bespoke suppliers like Divine appearing, who knows, this might be solved one day. I'll cover this in later post.
Different cup size systems
The bad news is that there are three mainstream systems and numerous niche ones for describing cup size... and the big three use the same letters to label different sizes of cup. The good news is that all cup systems are measured the same way.
In a woman, cup size is measured by looping a flexible tape horizontally but loosely around the fullest part of the breast (wearing a bra if necessary to correct any droop), reading off the number and subtracting the under breast measurement described in part one.
The three most popular systems are the UK one, the US/Canadian one and the EU scale. The Australian system for bras has a different way of measuring back size, but relies on the same system as the UK for cup size.
In all four, a one inch (2.5 cm) difference between the under bust and over breast measurement means an A cup, a two inch (5 cm) a B, a three inch (7.5 cm) difference a C, and four inches, or 10 cm a D.
Decades ago, a D cup was where many systems stopped, but as nutrition improved, breasts became larger and these days K cups are available in some ranges. At the other end of the scale, sub A cup sizes have appeared, and in these the letters work backward. So an AA cup is smaller than an A and an AAA is smaller than an AA.
All the common systems march in step up to a D, but after that, it gets funky. The UK cup system goes DD, E, F, FF, G, GG, H, HH, J, JJ and K - there is no I. The US/Canadian cup system goes DD (or E), DDD (or F), DDDD (or G), H, I, J and K. And just for fun, the EU system just goes E, F, G, H, I, J and K.
You can see the problem - a UK F is, approximately, the same size as a US/CA DDDD or G, and an EU H. Most of us aren't going to venture more than half a dozen steps into the cup size alphabet, but I include the word 'approximately' because the different standards don't necessarily match as far as cup volume change goes with each step. This is more pronounced in the larger cup sizes, and so for some EU brands, for instance Empreinte or Lejaby, an E cup overlaps somewhat with a UK E, when the conversion tables suggest the French bra should be a closer match for a UK DD.
Some trial and error may be involved, but since brands are internally consistent, it isn't difficult to get a feel for what size fits in each brand. The good news is that if you read the label, most bras show their band and cup size in the three common systems, so when in doubt, take a look.
How can I tell if a bra's cups fit my forms well enough?
As I wrote in the last post, bra sizing is so complex that many cis-women have trouble with this and end up wearing too large a band size and too small a cup size. Everything depends on getting the band size right, because that fixes the size of the wire in a bra.
If a form – or a real breast – fits a cup well, the gore of the bra should lie flat on the skin of the chest and the material of the cup should fit snugly without any wrinkles around the curvature of the form at the level of the nipple or below.
That's the ideal, but don't feel shy about wearing bras with forms where the gore doesn't quite touch the skin, where the material is a bit slack over the nipple area, or the upper part of the cup isn't completely in contact with the form, because bras are a compromise designed to work with as many shapes of breast as possible. If the gap between the gore and skin is wide enough to put a finger inside, though, your forms are too deep for the cups.
For a good fit, your forms should touch the sides of the cup at its widest point and the curve of the bottom of the cup should follow the curve of the form closely. Even with self-attaching forms, you don't want too much of the form showing above the neckline of the bra, because forms only have so much stiction and sooner or later, gravity will detach the apex, leaving a less than ideal cosmetic result.
A little bit of experiment will let you find brands that fit particular forms well and perhaps we should consider setting up a database here based on user experience?
