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Section one

Fit

Almost every complaint about a bra is a fit complaint wearing a different costume. Straps that dig, wires that stab, cups that gape: the cause is usually one size away.

A bra is a tension structure. A closed elastic loop goes round the ribcage, two cups sit on the front of that loop, and two straps run over the shoulders to stop the front tipping forward. That is the whole machine. Once the machine is understood, most fitting problems become obvious, because each symptom points at exactly one part that is doing too much or too little.

The part doing most of the work is the band. It is the only component in contact with the body all the way round, and it is the only one that can convert the weight of breast tissue into pressure spread over a wide area of ribcage. The straps cannot do that. They can only hang the front of the garment from two narrow points on the shoulders, which is why a bra held up by its straps produces sore shoulders and nothing else.

The two numbers

Sizing starts with two measurements taken with a soft tape. The first goes round the ribcage directly under the bust, snug and level. The second goes round the fullest part of the bust, level and without compression. The first number decides the band. The difference between the two decides the cup.

In the systems used across the United Kingdom, France, continental Europe and the United States, a cup letter is not a fixed volume. It is a description of that difference. A single inch of difference is roughly an A cup, two inches roughly a B, and so on up the alphabet. That is why a cup letter on its own means nothing at all: the same letter on a smaller band holds a visibly smaller volume.

  • How to measure sets out tape position and tension, which is where most errors are introduced.
  • The size calculator does the arithmetic and prints the conversion table underneath it.
  • Sister sizing explains why 32D and 34C are close cousins, and how to use that when a size is not stocked.

The four inch habit

An old fitting rule says to add four or five inches to the underbust measurement to get the band size. It made sense when band fabric had almost no stretch and the extra allowance was the only way to get the garment on. Modern band elastic recovers, so that allowance now produces a band several sizes too loose, which then rides up the back, transfers the load to the straps and creates every symptom people blame on their shoulders.

If the band rides up at the back, the band is too big. That is very nearly the only diagnosis, and it is right far more often than it is wrong.

Reading the evidence

A fitting room is a laboratory with poor lighting. The useful method is to run through the same checks every time, in the same order, so a judgement is being made rather than a guess.

  1. Fasten on the loosest hook. A new band should be firm there, leaving room to tighten as the elastic relaxes over its life.
  2. Turn sideways. The band should sit level from front to back, not angled up towards the shoulder blades.
  3. Slide two fingers under the band at the back. They should fit with resistance, not slip through and not refuse to enter.
  4. Look at the centre panel between the cups. On a wired bra it should sit flat against the breastbone.
  5. Look at the top edge of the cup. Wrinkling means too much volume. A visible cut across the breast means too little.
  6. Lift both arms above the head. If the whole garment travels upwards, the band is loose.

Signs of a bad fit takes each symptom in turn and gives the adjustment that fixes it. Band and cup goes further into why the two components behave the way they do.

Size is not stable

A size measured today is a snapshot. Weight moves, the cycle changes tissue volume over the course of a month, pregnancy and feeding change the ribcage as well as the bust, and elastic ages whether it is worn or not. Expecting one number to hold for a decade is the single most common reason a drawer stops working. Fit through change covers what shifts, how fast, and what is worth doing about it.

Two further complications are worth naming early. Almost nobody is symmetrical, and a difference of a cup size between left and right is unremarkable; fit the larger side and take up the slack on the other with the strap. And brands genuinely do not agree with each other, so the printed size that fits in one label may be one or even two steps away in another. That is a manufacturing fact, not a personal failing.