Free Bra Size Calculator to Find Your Perfect Fit

I’ve never had it easy with bra sizes. It became tougher to find a good fit after I became a mom. That’s why I spent some time going over bust sizes, band sizes, and how breast size changes during menstrual cycles, pregnancy, and postpartum. So, here’s a comprehensive bra size calculator that can help you get a fit that suits you!

Whether you want a firm or relaxed fit, you can choose for that too. No calculator gets it right for everyone on the first try, but this one will get you a lot closer than guessing.

Bra Size Calculator – How To Measure Your Bra Size

You have probably seen the claim that nearly 80% of women wear the wrong bra size. Fitting studies land anywhere between 70% and 100%, but they are small and mostly done in clinics and labs, so treat the number as a sign that sizing is hard rather than a statistic about you.

The measuring method most shops still use is a big part of why it feels so hard.

The calculator below asks for your bust three different ways instead of once, which is what makes it steadier than the tape-and-add-four method.

Bra Size Calculator

For the most accurate results, measure without a bra or shirt on.

❗ Please ensure all measurements are in inches for accurate calculations.

1. Measure Your Band Size

Wrap the measuring tape around your ribcage (under your bust where the bra band sits). Pull the tape as tightly as you want your bra to fit.

Select Band Size

2. Measure Your Bust Size

How to Measure Your Bust Properly (and Why It Matters!)

How to Measure Your Bust Properly: Getting the correct measurement is essential to ensure your bra fits well. Here’s how:

Step One: Grab a Soft Measuring Tape and take three measurements:

• Standing Bust: Measure while standing upright around the fullest part of your chest.
• Leaning Bust: Lean forward and measure around the fullest part of your bust.
• Lying Bust: Lie down and take one final measurement around the fullest part of your bust.

These three measurements together give us the most accurate result possible.

Upright Bust:

Stand or sit upright. Loosely wrap the tape around the fullest part of your bust.

Select Upright Bust Size Leaning Bust:

Lean forward about 90 degrees and wrap the tape around the fullest part of your bust.

Select Leaning Bust Size Lying Bust:

Lie down on your back and measure around the fullest part of your bust.

Select Lying Bust Size

3. Breast Fullness

Understanding Breast Fullness, and How These Selections Work

Understanding Breast Fullness: Breast fullness affects how a bra fits. This calculator adjusts the cup size based on your fullness type to ensure a snug fit without gaps or tightness.

• Center-Full: If your breasts are fuller in the center, we’ll slightly increase the cup size to prevent tightness.
• Average: Even fullness across the breast. No adjustments needed for your cup size.
• Side-Set: Fuller on the sides? We’ll decrease the cup size slightly to avoid gaps in the middle of the bra.

Center-Full Breasts

Normal/Average

Side-Set Breasts

4. Fit Preference

Understanding Fit Preference, and How It Affects Your Comfort

Understanding Fit Preference: Fit preference helps determine how snug or loose your bra band will feel. Choose based on your personal comfort level.

Normal Relaxed Firm

5. Choose Sizing System

Understanding Sizing Systems, and How This Calculator Works Across Regions

How Bra Sizes Differ Globally: Bra sizes are not universal. Different regions use different sizing systems. Choose your region to get the correct size.

U.S./Canada U.K. EU AUS/NZ

6. Calculate Your Size

Calculate Reset

Your Results

Your results will appear here.

Here's the Nitty Gritty Nerdy Stuff (if you're interested!)

Detailed calculations will appear here.

Show Detailed Calculations

Calculating...

How Do You Calculate Your Bra Size?

Measure snugly around your ribcage under the bust for the band, measure around the fullest part of your bust, then subtract the first from the second. Each inch of difference is one cup size.

• Band: round your underbust measurement to the nearest whole inch. US bands come in even numbers only, so an odd result means trying both neighbours.
• Cup: bust minus band. In US sizing, 1” = A, 2” = B, 3” = C, 4” = D, 5” = DD, 6” = DDD, and it keeps going.
• Worked example: a 34” underbust with a 38” bust is a 4” difference, which is a 34D.

Do You Still Add 4 Inches to Your Band Size?

No. Adding 4 or 5 inches to your underbust was a workaround for the stiff, barely elastic band fabric of the mid-1900s, and modern bands stretch. Start from your actual ribcage measurement instead.

• The difference is not small. A 32” underbust with a 38” bust reads as a 36B under the plus-four method and a 32DDD measured directly. Same body, four cup sizes apart.
• You can spot a plus-four band by how it behaves: it rides up your back during the day, and your shoulders end up carrying the weight that the band should be holding.
• Some department-store and heritage brand charts still tell you to add inches. If a brand’s own chart says to, follow it for that brand only, then check the fit in a mirror.

How Often Should You Re-Measure Your Bra Size?

Roughly every six months, and any time your bras start sitting differently. Retail fit guides such as Lane Bryant’s use the same six-month interval.

• Re-measure sooner after pregnancy, after weaning, after a weight change of ten pounds or so, or when you start or stop hormonal birth control.
• Measure at roughly the same point in your cycle each time. Wood and colleagues found bra fit correlated with menstrual cycle stage, so mid-cycle and pre-period measurements can disagree.
• If a band that used to fasten on the loosest hook now needs the tightest, the elastic is finished. That is a worn-out bra, not a new size.

Know Bra Size Charts and International Bra Sizes

A bra size chart is key to figuring out how your measurements translate into the right fit. While our easy bra size calculator does the work for you by using your band and bust measurements, having a chart on hand is super helpful when you’re offline or can’t use a calculator.

They also matter when you shop across borders, because a size printed on a label in one country is a different size in another.

Finding your perfect bra size is easier than you think, and we’re here to help! We’ve broken down how to understand both bra cup size and band size below.

• If you’re between sizes or find your measurements fall in an uncommon range, don’t worry! Knowing how to read bra sizing charts and guides will help you find the most comfortable fit always.
• Different countries use different sizing systems for bras. If you’re shopping internationally, it’s crucial to understand bra size conversion. For instance, UK, US, European, and Australian brands often have slightly different sizing standards.
  
  On averages: the most-cited US figure is 34DD, from a fitting survey of 40,000 customers run by the retailer Intimacy, up from 34B two decades earlier. The UK average is usually given as 36DD. Both come from sales and fitting appointments rather than a measured population, so read them as what gets bought, not what fits.
• A bra size conversion chart can help you ensure that you’re purchasing the correct size, no matter where you are shopping. Our bra size calculator includes bra size conversion features to make this process easier.

Understanding Bra Size

Bras are a $60 billion global market, and yet most high-street shops stock a range of roughly 32A to 38DD. Bodies come in a much wider range than that, which is why so many fittings end in a compromise rather than a fit.

Every bra size is two numbers doing two different jobs: a band around your ribcage, and a cup letter for volume. Get the band wrong and the cup will never sit right, however many letters you try.

1. Band Size (Frame Size)

Your band size is the measurement around your ribcage where the bra sits, and it carries most of the weight. If your straps are doing the lifting, the band is too loose. What that number is called changes by country, and so does what a label means by small, medium or large.

Refer to the table below for some size measurements, though some variation from the published measurements is possible.

2. Cup Size

Cup size is the gap between your bust and band measurements, at one cup per inch. The letter only means something attached to a band number.

Refer to the table below.

Example:

1. Measure your band size (underbust): Let’s say it’s 34 inches.
2. Measure your bust size (at the fullest part): Let’s say it’s 38 inches.
3. Find the difference between the bust and band size:
   38−34 = 4 inches.
4. Refer to the table for US cup size: A 4-inch difference corresponds to a D cup. In UK/AU sizing, this would also be a D cup.
5. For European sizing: convert the band, not the difference. A US 34 band is an EU 75, and cup letters match through D, so this is an EU 75D (and a French 90D). The centimetre table above uses the German EN 13402 grading, which steps cups differently and will hand you a different letter for the same body. When the two disagree, follow the brand’s own conversion chart.

This gives you a bra size rather than a breast size. The same body gets different letters in different systems and in different brands.

What Is a 37 Bra Size (or Any Odd Underbust Number)?

There is no 37 band in US or UK sizing, because bands run in even numbers: 30, 32, 34, 36, 38, 40. A 37-inch underbust means trying a 36 and a 38 and choosing by feel.

• Start with the 36 if you want firm support. New bands stretch with wear, so one that feels slightly snug on the loosest hook usually settles into the right tension.
• Change the cup letter when you change the band. With the same bust measurement, the 36 needs one cup letter more than the 38: a 38C and a 36D hold the same volume.
• The problem disappears in European sizing, where bands step in fives. A 37-inch underbust maps to an EU 80 or 85 band depending on which US band fits you better.

What Are Sister Sizes, and How Do You Use Them?

Sister sizes are bra sizes that hold the same cup volume on a different band. Go down a band and up a cup letter, or up a band and down a letter: 32D, 34C and 36B are all the same cup.

• Use them when the cups are right but the band is not. Band riding up your back means going down a band and up a cup (36C to 34D). Band digging into your ribs means going up a band and down a cup (36C to 38B).
• A cup letter is not a fixed volume. A 30D and a 40D are both D cups and hold very different amounts, which is why saying “I’m a D” tells a fitter almost nothing on its own.
• Brand charts from Thirdlove and Wacoal lay sister sizes out in rows. Any size sharing a row with yours is a sister size and worth trying when your usual size is out of stock.

Is a DD the Same as an E Cup?

It depends whose E you mean. A European E is the same cup as a US DD, but a British E is a size larger, equal to a US DDD.

• US cups stack the Ds: A, B, C, D, DD, DDD, then G, H, I, J.
• UK cups double the letters instead: A, B, C, D, DD, E, F, FF, G, GG, H.
• EU cups run a straight alphabet with no doubles: A, B, C, D, E, F, G. So one body is a US 34DD, a UK 34DD and an EU 75E, and ordering a UK 34E instead lands you a full cup too big. This is the single most common mistake when shopping British brands.

What Is My Bra Size in UK, EU, or Australian Sizing?

The band number always changes and the cup letter sometimes does. A US 34D is a UK 34D, an EU 75D, a French 90D and an Australian 12D.

• Bands: the US and UK share inch numbers. EU bands are (US band − 4) × 2.5, so US 34 is EU 75. France, Belgium and Spain add 15 to the EU number, making it FR 90. Australia and New Zealand subtract 22 from the US band, making it AU 12.
• Cups: identical in every system through D. Above D they split, so check the cup column of a conversion chart before you order rather than assuming your letter travels.
• Japanese and Chinese labels use EU centimetre bands but tend to cut cups shallower, so the converted size often runs about one cup small in practice.

Why is it Important to Wear the Correct Bra Size?

In a 2010 cross-sectional study, McGhee and Steele found that 85% of the 104 women assessed were wearing an ill-fitting bra, and that the sizes those women reached by self-selection or by standard shop measuring differed significantly from the size a professional fitter chose. An earlier study of young women by Wood, Cameron and Fitzgerald put the figure at 80%, with 70% wearing cups that were too small.

Both samples were small and both were Australian, so the exact percentage is soft. The direction is not. Cups that are too small and bands that are too loose are the two errors that keep turning up, and both are fixable at home with a tape measure.

• Many women are unaware of how cup and band sizes work, and some women are also shocked to learn that the common issues they face with bras are actually solvable (with the right bra size).
• The correct bra size can provide good support for your back and shoulders, and keep your chest and breasts feeling comfortable as you go about your day.

When your bra doesn’t fit quite right, it can be extremely irritating and can cause physical problems and discomfort too.

Here are a few ways to spot an ill-fitting bra, and more importantly, learn how to fix it with the right type of bra.

5 Signs Your Bra Doesn’t Fit – And How to Fix It

1. Inconvenient Underwires

• Problem: When your bra’s shape doesn’t sit well with the shape of your bust or if the underwire is too small, it can cause bruising on the chest, red marks, or constrict your breathing.
• Solution: Choose bras with flexible underwires and pay close attention to the material used. Make sure the underwire is soft and if you do not need that structured support, you can skip the underwire too.

2. Incorrect Cup Fits

• Problem: The cups might be too small, making your breasts spill over and out of the cups OR there may be a gap between the cups and your breasts, making you self-conscious about the fit.
• Solution: Please get a bra where the cups fit without breast overflow or gaps. For bra size fluctuations, make sure you get a bra with removable cups to adjust for the changes.

3. Poor-fitting Bands or Straps

• Problem: When a band or strap is too tight, it can rub or scrape your skin or cause irritation. This problem gets more noticeable if you live in humid or warm regions, causing frequent itching and more. A loose band can also ride up the back, making it uncomfortable.
• Solution: Find bras made with moisture-absorbing materials and breathable bands and straps. Also, measure the chest accurately to get a good band fit.

4. Shoulder and Back Pain

• Problem: When your bra is too tight or loose, your neck and shoulder can start to feel sore, and by the end of the day, you may face back pain too. This is more common for women with larger breasts.
• Solution: The trick is to make sure you distribute your breast weight evenly, so use bras with wider straps and get a snug band fit.

5. Slouching Posture

• Problem: When your bra does not support your frame well, it can make you slouch or hunch, and you may do this quite subconsciously.
• Solution: Pick from full-support bras like racerback bras, T-shirt bras, cross-back bras, shoulder support bras, among more to help maintain a good, strong posture that protects your spine for the long run. 

This is where our bra size calculator is practical because not only does it help you measure your bust and chest the right way, but it also helps you narrow down the correct bra size without too much hassle.

Can Breast Sizes Change With Time?

Absolutely! 

And not just during pregnancy or breastfeeding. They can change during the menstrual cycle, after weight changes, and more.

• Only the degree to which it changes differs from woman to woman. The most significant increase in breast size happens during pregnancy and breastfeeding, but weight gain can also be a major player.

That’s why it’s so helpful to have bras that can accommodate these changes. 

• Subtle fluctuations–like those that happen during the menstrual cycle–can be managed with a bra that has removable or adjustable cups. 
• For more noticeable changes, like from pregnancy or significant weight shifts, specialty bras like nursing bras or maternity bras, and expandable straps can help.

Know more about breastfeeding and pumping!

What Bra Size Should You Buy While Pregnant or Nursing?

Buy for the band and expect the cup to move more than once. The ribcage usually widens first during pregnancy, and cup volume jumps again when your milk comes in, generally between days three and five postpartum.

• Buy a band with spare hooks, or add a cheap bra extender, rather than sizing up in everything. The ribcage expansion of pregnancy largely reverses afterwards, and a whole drawer of 38s is an expensive way to find that out.
• Hold off on stocking up on nursing bras until around two weeks postpartum. Engorgement peaks in the first week, and the size you are then is not the size you settle at.
• Two or three well-fitting bras beat six that nearly fit. Anything that leaves deep marks, needs constant readjusting, or has a wire sitting on breast tissue rather than flat on your ribs is the wrong size, not something to break in.

Psst! There are also free online breast weight calculators that can give you a better sense of the size and weight of your breasts, too.

FAQs on Bra Size and Comfort

Concluding Thoughts on Bra Sizes

So many women I know and love have trouble finding the right bra size, and the band is usually where it goes wrong. A calculator narrows the field. The rest is a mirror check: band level and snug on the loosest hook, wire flat against your ribs rather than on breast tissue, no spilling and no gaping.

And dear mothers, don’t forget! Your breasts will get fuller, heavier, and can increase in size during pregnancies and breastfeeding. So, make sure you get bras that can adjust to these changes.

If a size feels close but not quite right, try its sister size before you try a different style, and re-measure every six months or so. And if the fit is fine but something still hurts, a lump, a burning pain, a fever, that is a conversation for your doctor rather than a sizing problem.