Your Bra Size Is A Myth

Your Bra Size Is A Myth

In a world of vanity sizes and mysterious designations like “medium”, you usually have to try clothes on before you have any clue if they fit. Bra sizing would seem to be different, since it involves numbers and maths, but I’m here with bad news: There is no such thing as Your One True Bra Size.

Illustration by TK. Photos by Travis Wise, VisualHunt and Joe Goldberg.

Nobody Even Agrees on How to Measure Yourself

It sounds scientific: You just measure your ribcage and your bust, and then use a simple formula to convert those measurements to a bra size consisting of a number and a letter (for example, “34B”). Here’s the typical formula, but as we will see, it varies:

  • Your band size (the number) comes from a measurement of your chest that does not include your breasts. Some instructions have you measure under your breasts; some ask you to measure above, basically right under your armpits.
  • Your cup size (the letter) comes from the difference between the band size and your bust measurement. In some versions of the formula, you simply subtract. In others, you add several centimetres (often 10) to your band size before comparing the two numbers.

The variations in the formula would all be fine if they worked out to give you about the same size, but they don’t. I did a little experiment to illustrate this.

I took my measurements above, at and under the bust and plugged them into a variety of calculators. Most instructions ask you to wear a bra that already fits you well, and in fact I have such a bra: A 34D in the Warner’s brand. Let’s see how the various calculators stack up:

Warner’s doesn’t have a calculator, but they do have an instructional video. I followed the instructions, and came up with 33D. Since band sizes only come in even numbers, that sounds like a pretty good endorsement for me taking a 34D in their brand.

The bottom line here: Following a brand’s instructions may help you find the right size bra in that brand, but don’t expect that size to help you find the right bra in another brand.

Cup Sizes Mean (Almost) Nothing

It’s tempting to assume that a cup size means the size of the cup. If you’re a D, for example, you might think any bra with a D cup should fit your breasts. But it turns out that a 32D and a 40D, for example, do not have anywhere near the same volume of space in the cup. People who sew bras need to buy the right size underwire for each cup, and this chart comparing underwire size to bra size reveals the relationship. A 32D (in this brand, anyway) uses the same size wire as a 38A.

This quirk is behind what’s known as sister sizes: Bra sizes that have the same fit in the cup but different fit in the band. If you wear a 36C, for example, a 34D is the same cup with a shorter band. Confusing? Look at this chart.

There’s a further confusion in mapping the letter sizes to measurements: Once you get beyond a D, everyone seems to have a different idea of what letter comes next. Some brands go right to E, F, G and so on, while others double up: DD and then DDD before moving on to another letter. HerRoom uses a metric they call Universal Cup Size to reconcile these differences between brands, so that can help if you’d like to try a new brand and want a clue for where to start. But what if the brand you want isn’t on their list, or if you’re at a brick-and-mortar store without a conversion chart?

Your Best Bet: Just Try Them On

You’re never going to get a complete answer about bra sizing just by poring over charts and calculators, in the hope you’ll ever be able to just walk into a store, pick up a bra in X size and take it home knowing it will fit comfortably. At some point you have to actually try the bra on and evaluate how well it fits. Briefly, you’re looking for something where:

  • The band sits horizontal (not pulling up or down at your back).
  • Your breasts fill out the cups without leaving gaps or spilling over.
  • The straps don’t slide off your shoulders, or dig in.
  • The wire (if there is one) doesn’t poke you; that could mean the cup is too small.

Going back to our initial experiment, where you start in a properly fitting bra: It isn’t cheating to just look at the tag. If it fits, it fits.

Besides the size of the bra, fit also depends on the shape. For example, some bras are cut for a rounder breast, and others for a more teardrop shaped breast. At the end of the day, bras are like any other clothes: The tag hints at how it will fit, but only trying it on will answer the question for sure.

This story has been updated since its original publication.


  • And when you find one that fits, buy it in every colour. Because it’s a rare and wonderful thing.

    • usually the company goes out of business as soon as you have the perfect size garment or they change the styling so you can’t buy it any more.

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