This calculator estimates bra size based on bust size and band size (frame size). To ensure accuracy, measure to the nearest ¼ inch or ½ cm. This calculator provides results for the United States, the United Kingdom, European Union, France, Belgium, Spain, Australia, and New Zealand.
The bust size is the loose circumference measured around the chest over the fullest part of the breasts, while standing straight with arms to the side, and wearing a properly fitted bra.
The band or frame size is the firm circumference, fitted not tightly, measured directly underneath the breasts.
Use the following to convert bra sizes between different locations.
The bra size calculator estimates your bra size from just two measurements — your bust size and your band (frame) size — and instantly shows the equivalent size in the sizing systems used across the United States, the United Kingdom, the European Union, France, Belgium, Spain, Australia, and New Zealand. Because bra sizing is notoriously inconsistent between countries and even between brands, having every regional size in one place makes it far easier to shop online, buy while traveling, or simply understand what all those numbers and letters mean. The page also includes a dedicated bra size converter that translates a known size from one region directly into all the others.
Enter your measurements in inches or centimeters, click Calculate, and you will see a full table of results. Keep in mind that the output is a starting point: bra fit varies by brand, style, and body shape, so the best approach is always to try bras on or get a professional fitting. Still, knowing your calculated size narrows the search dramatically and helps you recognize when a bra simply is not made to fit you.
Accurate measurements are the whole game. Use a soft cloth tape measure, stand up straight with your arms relaxed at your sides, and measure to the nearest quarter inch or half centimeter. It helps to measure in front of a mirror to keep the tape level, and to wear a well-fitting, non-padded bra when taking the bust measurement.
The difference between your bust and band measurements is what sets the cup size, so measuring both carefully — and consistently — is essential. If your results seem off, re-measure; a tape that rides up in the back or is pulled too tightly is the most common source of error.
Bra size has two parts: a band number and a cup letter. The band number comes from your underbust measurement, and the cup letter comes from the difference between your bust and band measurements.
In the US and UK systems, the band number is based on your underbust measurement in inches, rounded to the nearest even number (28, 30, 32, 34…). This calculator uses that "true to body" method for its primary result. You may also encounter the older "+4" (or "+5") method, in which four or five inches are added to the underbust measurement before rounding — a technique some traditional fitters and a few manufacturers still use. Because it produces a looser band, the calculator shows the "+4" results separately so you can compare. European (EN 13402), French, Belgian, and Spanish systems use the underbust measurement in centimeters to derive their band numbers instead.
The cup letter is determined by subtracting your band measurement from your bust measurement. In the inch-based systems, roughly each additional inch of difference is one cup size up: about 1 inch is an A cup, 2 inches a B, 3 inches a C, 4 inches a D, and so on. The European system works in centimeters, with roughly every 2 centimeters of difference equaling one cup step, which is why the same body can be labeled with a different cup letter in Europe than in the US or UK. Cup letters themselves are not standardized across regions — a US "DDD" corresponds to a UK "E" and an EU "F," for example — which is a major reason bra shopping across borders is so confusing.
After you calculate, the results table lists your estimated size in each major system:
If you already know your bra size in one country's system and just want the equivalent elsewhere, use the Bra Size Converter. Choose the location your known size belongs to, pick the band size and cup, and click Convert. The tool returns your size in every other supported system at once. This is perfect for online shopping from international retailers, reading care labels on imported bras, or figuring out what to ask for in a shop abroad. Because the converter maps sizes position-by-position through standardized tables, it gives clean, consistent translations between regions.
Surveys and studies frequently claim that anywhere from 70% to 85% of women wear an incorrectly fitted bra. Even if those figures are inflated by inconsistent research methods, poor fit is undeniably common — and it has real consequences. A band that is too loose or a cup that is too small can cause shoulder, neck, and back pain, skin irritation, poor posture, and headaches, while an ill-fitting bra simply looks and feels wrong under clothing. The lack of standardization between brands and countries is a big part of the problem: the same woman can be a 34C in one label and a 32DD in another. Understanding your measured size — and how it translates across systems — is the first step to finding bras that actually fit.
Even with careful measuring, you will find that your ideal size varies from brand to brand and style to style. Manufacturers cut their bras differently, use different materials with different amounts of stretch, and sometimes engage in "vanity sizing." A push-up, a balconette, a sports bra, and a full-coverage bra from the same brand can all fit differently at the identical labeled size. This is why the calculator's result is best treated as a well-informed starting point rather than an absolute. Once you know your calculated size, try the size the calculator suggests along with the "sister sizes" immediately above and below it — going down a band and up a cup, or up a band and down a cup, keeps roughly the same cup volume and often solves fit problems.
"Sister sizes" are bra sizes that share the same cup volume but have different band numbers. As the band gets larger, the cup letter must get smaller to keep the same volume, and vice versa. For example, a 34C, a 32D, and a 36B all have very similar cup volumes; they differ mainly in how tight the band is. If a bra's cups fit well but the band feels too tight or too loose, switching to a sister size is often the fix. Knowing your sister sizes dramatically expands your options when a particular size is sold out or a brand runs small or large.
One of the biggest sources of confusion in bra shopping is that almost every region measures and labels sizes differently. The US and Canada use a band number in inches paired with cup letters that double up at the larger end (D, DD, DDD, and so on). The UK shares the same band numbers but progresses through single letters with doubled variants (D, DD, E, F, FF, G…), so a US "DDD" is a UK "E." The European EN 13402 standard expresses the band in centimeters and steps the cup roughly every two centimeters, which produces yet another lettering pattern. France, Belgium, and Spain use band numbers that run 15 higher than the EU figure for the same body — an EU 75 is an FR 90 — while sharing the EU cup letters. Australia and New Zealand use a dress-code number similar to the UK dress size, combined with UK-style cups. Italy uses its own numeric system (often written with Roman-numeral-like cup codes), and Japan and much of Asia use centimeter-based systems close to the EU approach. Because there is no single global standard, a woman who is a 34C in the US might see 34C, 75E, 90E, and a size 12 on labels from different countries — all describing the same bra. This calculator and its converter exist precisely to cut through that confusion by putting every system side by side.
A well-fitting bra only stays that way if it is looked after, because the elastic in the band and straps is what does most of the work. To extend the life and fit of your bras, hand wash them when you can, or use a lingerie bag on a gentle cycle with cold water, and always air dry rather than tumble drying — heat destroys elastic quickly. Rotate between several bras rather than wearing the same one day after day, giving the elastic at least a day to recover between wears. Fasten bras on the loosest hook when they are new; as the band naturally stretches over months of wear, move to tighter hooks to maintain support. Most bras last somewhere between six months and a year of regular wear before the band loosens enough to compromise fit, which is another good reason to re-measure and recalculate your size periodically. Storing bras flat or fastened, with the cups nested rather than folded inward, helps molded cups keep their shape as well.
Two: your bust size (the loose circumference around the fullest part of your breasts) and your band size (the firm circumference directly under your breasts). You can enter both in inches or centimeters.
Cup sizing is not standardized worldwide. The US and UK step cups by roughly one inch of bust-to-band difference, while the EU steps by roughly two centimeters, and each region uses a different sequence of letters. That is why the same body can be a US "DDD," a UK "E," and an EU "F." The calculator shows all of them so you can compare.
It is an older fitting method that adds four or five inches to your underbust measurement before rounding to get the band size. It produces a looser band than the modern true-to-body method. Only a few manufacturers still use it, so the calculator shows those results separately, marked with an asterisk.
It is a solid starting point based on standard sizing formulas, but no calculator can account for every brand's cut, the style of bra, or your individual shape. Use the result to narrow your search, then try the suggested size along with its sister sizes, or get a professional fitting.
The bust measurement should be larger than the band measurement, because it is taken over the fullest part of the breasts. If it comes out smaller, the measurement was likely taken incorrectly — re-measure your bust over the fullest point while standing straight, keeping the tape level.
Your size can change with weight fluctuations, pregnancy, breastfeeding, hormonal changes, and age. It is a good idea to re-measure every six to twelve months, or any time your bras start to feel different, before buying new ones.
This Bra Size Calculator is provided for general informational purposes only. Results are estimates based on standard sizing conventions and will vary between brands, styles, and individual body shapes. The calculator is not a substitute for trying bras on or for a professional fitting. Always confirm fit before purchasing.