How to Measure Your Bra Size at Home, the Right Way

Let’s get you fitted, shall we?

When was the last time you measured your bra size? If it was more than six months ago, there’s a decent chance that the number/letter combo you have in your head might not be 100% accurate.

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“Most people don’t know what those letters and numbers mean on their bra,” says Cora Harrington, author of In Intimate Detail: How to Choose, Wear, and Love Lingerie and editor-in-chief of The Lingerie Addict. “People aren't able to conceptualize those bra measurements as essentially a substitute for their approximate breast volume.”

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In short, the number represents your band size. The letter corresponds with your cup size, which is the difference between the largest part of your bust and your band size (more on that later). Taken together, you’ve got your bra size — or at least a version of it, because every bra differs slightly from manufacturer to manufacturer, Harrington notes. So you might have a better fit in a different size than what was originally measured. And that’s OK!

Of course, any lingerie boutique or department store clerk can take your measurements for you, but we live in the age of DIY and online shopping, so knowing how to properly take your own measurements is a true sign of adulting (and it’s more convenient). All you’ll need is measuring tape (the soft kind used for clothing) and a way to record your numbers. A well-fitting bra is just a few simple calculations away!

STEP 1: MEASURE YOUR BAND SIZE

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You’ll want to be completely topless for this to ensure you’re measuring your breasts at their most natural, Harrington says — no padding, binding, lifting, or constricting. Take the measuring tape and wrap it around your ribcage, just under your bust. The measuring tape should be parallel to the ground.

You should be able to fit a finger under the measuring tape. “If you’re pulling your tape measure too tightly, you might wind up getting a bra band that’s too tight,” Harrington says. “If you have a larger or heavier bust, you probably do want a bra band that’s a little bit tight, but let’s start off with accurate measurements first. If you have a smaller bust, having a bra band that’s too tight can be very uncomfortable, especially if you are thinner and have less cushion on your rib cage because the bra band is resting directly on those bones.”

Round the measurement to the nearest whole number and you’ve got your band size. Depending on the manufacturer, you may need to add four if the measurement is even and add five if the number is odd. So if you measured 34 inches, your band size would be 38; if you measured 27 inches, your band size would be 32. Historically, this has been standard practice in bra measuring and manufacturing — and no one is really sure why. Some speculate the “plus-four rule” was to accommodate for breathing room when bras were made out of un-stretchy material like silk and satin. Popular bra-fit community r/ABraThatFits traced the plus-four method back to the 1960s when bra measurement practices changed. Again, it’s important to consult each manufacturer's fit guide to determine if you’ll need to do this addition.

STEP 2: MEASURE YOUR BUST SIZE

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More specifically, measure the fullest part of your bust. Again, keeping the measuring tape parallel with the ground, wrap the tape around your body at nipple height “because that tends to be where your bust projects most from your body,” Harrington says.

For folks whose breast tissue is fuller at the bottom or if your bust is less projected, Harrington suggests that you might need to bend at the waist to get an accurate nipple measurement. You can also measure your bust while lying on your back if your mobility prevents you from standing up or bending over.

STEP 3: FIND YOUR CUP SIZE

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Take your bust measurement (usually the bigger number) and subtract your band measurement. This number corresponds with your cup size. If your bust measurement and band measurement are the same number, you’re an AA cup. If there’s a 1-inch difference between bust and band you’re an A cup; 2-inch difference is a B cup, 3 inches is a C cup, 4 inches is a D cup, and so on. For example, if your bust measurement is 37 inches and your band is 33 inches, you would be a D cup because of the 4-inch difference.

STEP 4: PUT IT ALL TOGETHER

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Remember when we measured our band size in step one? Take that number and drop it in front of the cup size you just calculated in step three. Using the example from the last step, the bra size would be a 33D.

STEP 5: DON’T GET ATTACHED

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Just as our clothing sizes change throughout our lives — and from brand to brand — so too do bra sizes. “There’s way too much variability in the lingerie industry and in the way bras fit to get extremely attached to one bra size,” Harrington says. “You should buy the bra that works in the size that works for you, which might not be the size that you measured yourself at. I do think that often people will make their bra size a part of their identity, and the concern when you do that is you may find yourself not getting the best fit you can get either because your identity is so wrapped up in being a C or a D cup when really you could be better suited to an F cup.”

STEP 6: REPEAT, OFTEN

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Because our bodies are constantly changing, it’s important to regularly measure your bra size. Harrington recommends every three to six months works to re-measure. Depending where you are in your cycle, the time of year, or if you’ve just given birth, you might get a size that seems way off from the last time you measured. That’s normal. “A lot of people might go up or down a cup size or two based on where they are in their cycle,” Harrington says. “Having different measurements doesn't mean you need to go out and buy all new bras, but it’s good to get familiar with what your natural range of measurements might be.”

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Also, while we’re here, these exact same steps will get you your sports bra and bralette measurements for manufacturers/bra styles that uses band and cup size, Harrington notes. For those that use XS–XL sizing, like some of Nike’s bras, for example, consult the manufacturer’s sizing guide, which will translate your cup/band measurements into letter sizing.