Determining the correct bra size (also known as brassiere measurement or bust size) is the process manufacturers engage in to design and manufacture bras that correctly fit a majority of women, and for individual women, the process of identifying a correctly fitting bra. Bra sizes usually consist of one or more letters indicating the breast cup size and a number, indicating a band size around the woman's torso. Bra cup sizes were invented in 1932 and band sizes became popular in the 1940s.
- Measurement method origins
- Cup design origins
- Band measurement origins
- Other innovations
- Consumer fitting
- Larger breasts and bra fit
- Bad bra fit symptoms
- Obtaining best fit
- Confirming bra fit
- Bra size calculator
- Consumer measurement difficulties
- Asymmetrical breasts common
- Breast volume variation
- Increasing breast size
- Consumer measurement methods
- Band measurement methods
- Underbust 0
- Underbust 4
- Sizing chart
- Above the breasts
- Cup measurement methods
- Cup sizes vary
- Measuring cup size without a bra
- Consumer fit research
- Manufacturer design standards
- AustraliaNew Zealand
- United States and Canada
- Continental Europe
- South KoreaJapan
- Advertising and retail influence
- Calculating cup volume and breast weight
The shape, size, position, symmetry, spacing, firmness, and amount of sagging of individual women's breasts vary considerably. Manufacturers' bra size labeling systems vary from country to country because no international standards exist. Even within a single country, one study found that the bra label size was consistently different from the measured size. As a result, about 25% of women have a difficult time finding a properly fitted bra. Some women choose to buy custom-made bras due to the unusual size or shape of their bust.
Measurement method origins
Parisienne Madeleine Gabeau received a United States patent on 21 November 1911 for a brassiere with soft cups and a metal band that supported and separated the breasts. To avoid the prevailing fashion that created a single "monobosom", her design provided "that the edges of the material d may be carried close along the inner and under contours of the breasts, so as to preserve their form, I employ an outlining band of metal b which is bent to conform to the lower curves of the breast."
Cup design origins
The term "cup" was not used to describe bras until 1916 when two patents were filed.
In October 1932, the S.H. Camp and Company were the first to measure cup size by the letters of the alphabet, A, B, C, and D, though the letters represented how pendulous the breasts were and not their volume. Camp's advertising in the February 1933 issue of Corset and Underwear Review featured letter-labeled profiles of breasts. Cup sizes A through D were not intended to be used for larger-breasted women.
In 1937, Warner introduced its Alphabet Bra with four cup sizes (A, B, C and D) to its product descriptions. Before long, these cup sizes got nicknames: egg cup, tea cup, coffee cup and challenge cup. Two other companies, Model and Fay-Miss (renamed in 1935 as the Bali Brassiere Company) followed, offering A, B, C and D cup sizes in the late 1930s. Catalog companies continued to use the designations Small, Medium and Large through the 1940s. Britain did not adopt the American cups in 1933, but resisted using cup sizes for its products until 1948. The Sears Company finally applied cup sizes to bras in its catalog in the 1950s.
Band measurement origins
Adjustable bands were introduced using multiple hook and eye closures in the 1930s. Prior to the widespread use of bras, the undergarment of choice for Western women was a corset. To help women meet the perceived ideal female body shape, corset and girdle manufacturers used a calculation called hip spring, the difference between waist and hip measurement (usually 10–12 inches).
The band measurement system was created by U.S. bra manufacturers just after World War II.
The underwire was first added to a strapless bra in 1937 by André, a custom-bra firm. Patents for underwire-type devices in bras were issued in 1931 and 1932, but were not widely adopted by manufacturers until after World War II when metal shortages eased.
In the 1930s, Dunlop chemists were able to reliably transform rubber latex into elastic thread. After 1940, "whirlpool," or concentric stitching was used to shape the cup structure of some designs. The man-made fibres were quickly adopted by the industry because of their easy-care properties. Since a brassiere must be laundered frequently, easy-care fabric was in great demand.
Pendulous breasts can make it difficult for a person to properly fit a bra. For best results, the breasts should be measured twice: once when standing upright, once bending over at the waist with the breasts hanging down. If the difference between these two measurements is more than 10 cm, then the average is chosen for calculating the cup size. A number of reports, surveys and studies in different countries have found that between 80% to 85% of women wear incorrectly fitted bras.
In November 2005, Oprah Winfrey produced a show devoted to bras and bra sizes, during which she talked about research that eight out of ten women wear the wrong size bra.
Larger breasts and bra fit
When purchasing bras, larger-breasted women usually have difficulty selecting a well-fitting bra. Buxom women are more likely than smaller-breasted women to wear an incorrectly sized bra. They tend to buy bras that are too small, while smaller-breasted women tend to purchase bras that are too large. Studies have revealed that the most common mistake made by women when selecting a bra was to choose too large a back band and too small a cup, for example, 38C instead of 34E, or 34B instead of 30D.
As breasts become larger, their shape and the distribution of tissue within them changes. The breasts may become ptotic. This makes measurements increasingly unreliable. The heavier a person's build, the more difficult it is to obtain accurate measurements, as measuring tape sinks into the flesh more easily.
In a study conducted in the United Kingdom of 103 women seeking mammoplasty, researchers found a strong link between obesity and inaccurate back measurement. They concluded that "obesity, breast hypertrophy, fashion and bra-fitting practices combine to make those women who most need supportive bras the least likely to get accurately fitted bras."
One issue that complicates finding a correctly fitting bra is that band and cup sizes are not standardized, but vary considerably from one manufacturer to another, resulting in sizes that only provide an approximate fit. Women cannot rely on labeled bra sizes to identify a bra that fits properly. Scientific studies show that the current system of bra sizing may be inaccurate.
Manufacturers cut their bras differently, so, for example, two 34B bras from two companies may not fit the same person. Customers should pay attention to which sizing system is used by the manufacturer. The main difference is in how cup sizes increase, by 2 cm or 1 inch (= 2.54 cm, see below). Some French manufacturers also increase cup sizes by 3 cm. Unlike dress sizes, manufacturers do not agree on a single standard.
British bras currently range from A to LL cup size (with Rigby&Peller recently introducing bras by Elila which go up to US-N-Cup), while most Americans can find bras with cup sizes ranging from A to G. Some brands (Goddess, Elila) go as high as N, a size roughly equal to a British JJ-Cup. In continental Europe, Milena Lingerie from Poland produces up to cup R. Larger sizes are usually harder to find in retail outlets. As the cup size increases, the labeled cup size of different manufacturers' bras tend to vary more widely in actual volume. One study found that the label size was consistently different from the measured size.
Even medical studies have attested to the difficulty of getting a correct fit. Research by plastic surgeons has suggested that bra size is imprecise because breast volume is not calculated accurately:
The current popular system of determining bra size is inaccurate so often as to be useless. Add to this the many different styles of bras and the lack of standardization between brands, and one can see why finding a comfortable, well-fitting bra is more a matter of educated guesswork, trial, and error than of precise measurements.
The use of the cup sizing and band measurement systems has evolved over time and continues to change. Experts recommend that women get fitted by an experienced person at a retailer offering the widest possible selection of bra sizes and brands.
Bad bra-fit symptoms
If the straps dig into the shoulder, leaving red marks or causing shoulder or neck pain, the bra band is not offering enough support. If breast tissue overflows the bottom of the bra, under the armpit, or over the top edge of the bra cup, the cup size is too small. Loose fabric in the bra cup indicates the cup size is too big. If the underwires poke the breast under the armpit or if the bra's center panel does not lie flat against the sternum, the cup size is too small. If the band rides up the torso at the back, the band size is too big. If it digs into the flesh, causing the flesh to spill over the edges of the band, the band is too small. If the band feels tight, this may be due to the cups being too small; instead of going up in band size a person should try going up in cup size. Similarly a band might feel too loose if the cup is too big. It is possible to test whether a bra band is too tight or too loose by reversing the bra on her torso so that the cups are at the back and then check for fit and comfort. Generally, if the wearer must continually adjust the bra or experiences general discomfort, the bra is a poor fit and she should get a new fitting.
Obtaining best fit
Bra experts recommend that women, especially those whose cup sizes are D or larger, get a professional bra fitting from the lingerie department of a clothing store or a specialty lingerie store. However, even professional bra fitters in different countries including New Zealand and the United Kingdom produce inconsistent measurements of the same person. There is significant heterogeneity in breast shape, density, and volume. As such, current methods of bra fitting may be insufficient for this range of chest morphology.
A 2004 study by Consumers Reports in New Zealand found that 80% of department store bra fittings resulted in a poor fit. However, because manufacturer's standards widely vary, women cannot rely on their own measurements to obtain a satisfactory fit. Some bra manufacturers and distributors state that trying on and learning to recognize a properly fitting bra is the best way to determine a correct bra size, much like shoes.
Bra fitters generally agree that a correctly fitting bra should meet the following criteria:
Confirming bra fit
One method to confirm that the bra is the best fit has been nicknamed the Swoop and Scoop. After identifying a well-fitting bra, the woman bends forward (the swoop), allowing their breasts to fall into the bra, filling the cup naturally, and then fastening the bra on the outermost set of hooks. When the woman stands up, she uses the opposite hand to place each breast gently into the cup (the scoop), and she then runs her index finger along the inside top edge of the bra cup to make sure her breast tissue does not spill over the edges.
Experts suggest that women choose a bra band that fits well on the outermost hooks. This allows the wearer to use the tighter hooks on the bra strap as it stretches during its lifetime of about eight months. The band should be tight enough to support the bust, but the straps should not provide the primary support.
Bra size calculator
There are many online bra size calculator tools, mostly you will find on lingerie website. But one major bra size problem is that it varies according to brand. So even if you know the bra size of some particular brand, you should get yourself measured if you're buying bra from some other brand.
Consumer measurement difficulties
A bra is one of the most complicated articles of clothing to make. A typical bra design has between 20 and 48 parts, including the band, hooks, cups, lining, and straps. Major retailers place orders from manufacturers in batches of 10,000. Orders of this size require a large-scale operation to manage the cutting, sewing and packing required.
Constructing a properly fitting brassiere is difficult. Adelle Kirk, formerly a manager at the global Kurt Salmon management consulting firm that specializes in the apparel and retail businesses, said that making bras is complex:
Bras are one of the most complex pieces of apparel. There are lots of different styles, and each style has a dozen different sizes, and within that there are a lot of colors. Furthermore, there is a lot of product engineering. You've got hooks, you've got straps, there are usually two parts to every cup, and each requires a heavy amount of sewing. It is very component intensive.
Asymmetrical breasts common
Obtaining the correct size is complicated by the fact that up to 25% of women's breasts display a persistent, visible breast asymmetry, which is defined as differing in size by at least one cup size. For about 5% to 10% of women, their breasts are severely different, with the left breast being larger in 62% of cases. Minor asymmetry may be resolved by wearing a padded bra, but in severe cases of developmental breast deformity—commonly called "Amazon's Syndrome" by physicians, may require corrective surgery due to morphological alterations caused by variations in shape, volume, position of the breasts relative to the inframammary fold, the position of the nipple-areola complex on the chest, or both.
Breast volume variation
Obtaining the correct size is further complicated by the fact that the size and shape of women's breasts change, if they experience menstrual cycles, during the cycle and can experience unusual or unexpectedly rapid growth in size due to pregnancy, weight gain or loss, or medical conditions. Even breathing can substantially alter the measurements.
Some women's breasts can change shape by as much as 20% per month:
"Breasts change shape quite consistently on a month-to-month basis, but they will individually change their volume by a different amount ... Some girls will change less than 10% and other girls can change by as much as 20%." Would it be better not to wear a bra at all then? "... In fact there are very few advantages in wearing existing bras. Having a bra that's generally supportive would have significant improvement particularly in terms of stopping them going south ... The skin is what gives the breasts their support"
Increasing breast size
In 2010, the most common bra size sold in the UK was 36D. In 2004, market research company Mintel reported that bust sizes in the United Kingdom had increased from 1998 to 2004 in younger as well as older consumers and that the shift was not limited to overweight women, while a more recent study showed that the most often sold bra size in the US in 2008 was 36D.
Researchers also said more women wear the correct—bigger—size now, spurred on by shows like BBC 1's What Not To Wear and Channel 4's How To Look Good Naked.
Consumer measurement methods
Bra retailers recommend several methods for measuring band and cup size. These are based on two primary methods, either under the bust or over the bust, and sometimes both. Calculating the correct bra band size is complicated by a variety of factors. The American National Standards Institute states that while a voluntary consensus of sizes exists, there is much confusion to the ‘true’ size of clothing. As a result, bra measurement can be considered an art and a science. Online shopping and in-person bra shopping experiences may differ because online recommendations are based on averages and in-person shopping can be completely personalized so the shopper may easily try on band sizes above and below her between measured band size. For the woman with a large cup size and a between band size, they may find their cup size is not available in local stores so may have to shop online where most large cup sizes are readily available on certain sites. Others recommend rounding to the nearest whole number.
Band measurement methods
There are several possible methods for measuring the bust.
A measuring tape is pulled around the torso at the inframammary fold. The tape is then pulled tight while remaining horizontal and parallel to the floor. The measurement in inches is then rounded to the nearest even number for the band size.
This method begins the same way as the underbust +0 method, where a measuring tape is pulled tight around the torso under the bust while remaining horizontal. If the measurement is even, 4 is added to calculate the band size. If it is odd, 5 is added. Kohl’s uses this method for its online fitting guide.
Currently, many large U.S. department stores determine band size by starting with the measurement taken underneath the bust similar to the aforementioned underbust +0 and underbust +4 methods. A sizing chart or calculator then uses this measurement to determine the band size. Band sizes calculated using this method vary between manufacturers, although the band sizes generally lie in between band sizes that would result from the underbust +0 method and underbust+4 method.
Above the breasts
Victoria's Secret uses this method, where a measuring tape is pulled around the torso under the armpit and above the bust. Because band sizes are most commonly manufactured in even numbers, the wearer must round to the closest even number.
Cup measurement methods
Bra-wearers can calculate their cup size by finding the difference between their bust size and their band size. The bust size, bust line measure, or over-bust measure is the measurement around the torso over the fullest part of the breasts, with the crest of the breast halfway between the elbow and shoulder, usually over the nipples, ideally while standing straight with arms to the side and wearing a properly fitted bra. This practice assumes the current bra fits correctly. The measurements are made in the same units as the band size, either inches or centimetres. The cup size is calculated by subtracting the band size from the over-the-bust measurement.
Cup sizes vary
Cup sizes vary from one country to another. The larger the cup size, the bigger the variation.
Surveys of bra sizes tend to be very dependent on the population studied and how it was obtained. For instance, one U.S. study reported that the most common size was 34B, followed by 34C, that 63% were size 34 and 39% cup size B. However, the survey sample was drawn from 103 Caucasian student volunteers at a Midwest U.S. university aged 18–25, and excluded pregnant and nursing women.
Bra maker Triumph conducted a survey in 2007 to determine the percentage of women wearing four cup sizes, and found that 57% of British women, more than any other country, need a D cup.
Measuring cup size without a bra
Bra-wearers who have difficulty calculating a correct cup size may be able to find a correct fit using a method adopted by plastic surgeons. Using a flexible tape measure, position the tape at the outside of the chest, under the arm, where the breast tissue begins. Measure across the fullest part of the breast, usually across the nipple, to where the breast tissue stops at the breast bone. This measuring approach assumes that the breasts are not so large or pendulous that they sag significantly, making measuring across the fullness of the breast impractical. Only women whose breasts are firm and spherical can measure without a bra.
Conversion of the measurement to cup size is as follows:
These cup measurements are only correct for a 34-inch band because cup size is relative to band size. The volume of a brassiere cup is the same for 30D, 32C, 34B, and 36A, though the shape of each cup may be different. These related bra sizes of the same cup volume are called sister sizes. It is sometimes possible that two adjacent sister sizes will both fit a person, since the cup volume is the same, while the band size can be adjusted to a small degree by using the hook and eye fasteners in the bra clasp.
Consumer fit research
A 2012 study by White and Scurr University of Portsmouth compared method that adds 4 to the band size over-the-bust method used in many United Kingdom lingerie shops with and compared that to measurements obtained using a professional method. The study relied on the professional bra-fitting method described by McGhee and Steele (2010).
The study utilized a five-step approach to obtain the best fitting bra size for an individual. The study measured 45 women using the traditional selection method that adds 4 to the band size over-the-bust method. Women tried bras on until they obtained the best fit based on professional bra fitting criteria. The researchers found that 76% of women overestimated their band and 84% underestimated their cup size. When women wear bras with too big a band, breast support is reduced. Too small a cup size may cause skin irritation. They noted that "ill-fitting bras and insufficient breast support can lead to the development of musculoskeletal pain and inhibit women participating in physical activity." The study recommended that women should be educated about the criteria for finding a well-fitting bra. They recommended that women measure under their bust to determine their band size rather than the traditional over the bust measurement method.
Manufacturer design standards
Bra-labeling systems used around the world are at times misleading and confusing. Cup and band sizes vary around the world. In countries that have adopted the European EN 13402 dress-size standard, the torso is measured in centimetres and rounded to the nearest multiple of 5 cm. Bra-fitting experts in the United Kingdom state that many women who buy off the rack without professional assistance wear up to two sizes too small.
Manufacturer Fruit of the Loom attempted to solve the problem of finding a well-fitting bra for asymmetrical breasts by introducing Pick Your Perfect Bra, which allow women to choose a bra with two different cup sizes, although it is only available in A through D cup sizes.
There are several sizing systems in different countries. Most use the chest circumferences measurement system and lettered cup sizes, but there are some significant differences. Many bras available come in only 36 sizes.
The UK uses the inch-system, this means that the difference in chest circumference between the cup sizes is always one inch, or 2.54 cm. The difference between 2 band sizes is 2 inches or 5.08 cm.
Leading brands and manufacturers including Panache, Bestform, Gossard, Freya, Curvy Kate, Bravissimo and Fantasie, which use the British standard band sizes 28-30-32-34-36-38-40-42-44, and so on. Cup sizes are designated by AA-A-B-C-D-DD-E-F-FF-G-GG-H-HH-J-JJ-K-KK-L.
However, some clothing retailers and mail order companies have their own house brands and use a custom sizing system. Marks and Spencers uses AA-A-B-C-D-DD-E-F-G-GG-H-J, leaving out FF and HH. As a result, their J-Cup is equal to a British standard H-cup. Evans and ASDA sell bras (ASDA as part of their George clothing range) whose sizing runs A-B-C-D-DD-E-F-G-H. Their H-Cup is roughly equal to a British standard G-cup.
Some retailers reserve AA for young teens, and use AAA for ladies.
Australia and New Zealand use a permutation of the British system. Cup sizes are the same, but Australia's bra band measurement system is based on dress sizing charts. However, dress sizes and cuts are calculated for B and C cups only, so basing the choice of band size upon dress size is not an accurate way to get the bra size. Depending upon a person's build, a size 16 may wear a 16 C (UK 40 C), a 14 DD, 12 F or a 10 G (UK 34 G) underneath their clothes, because all bra sizes are made for the same chest circumference of approx. 40 inches.
United States and Canada
Bra-sizing in the United States and Canada is very similar to the United Kingdom. Band sizes use the same designation in inches and the cups also increase by 1-inch-steps. However, some manufacturers use conflicting sizing methods. Some label bras beyond a C cup as D-DD-DDD-DDDD-E-EE-EEE-EEEE-F…, some use the variation: D1, D2, D3, D4, D5..... but many use the following system: A, B, C, D, DD, DDD, G, H, I, J, K, L, M, N, O. and others label them like the British system D-DD-E-F-FF… Comparing the larger cup sizes between different manufacturers can be difficult.
In 2013, underwear maker Jockey International offered a new way to measure bra and cup size. It introduced a system with ten cup sizes per band size that are numbered and not lettered, designated as 1-36, 2-36 etc. The company developed the system over eight years, during which they scanned and measured the breasts and torsos of 800 women. Researchers also tracked the women's use of their bras at home. To implement the system, women must purchase a set of plastic cups from the company to find their Jockey cup size. Some analysts were critical of the requirement to buy the measurement kit, since women must pay about USD$20 to adopt Jockey's proprietary system, in addition to the cost of the bras themselves.
In Continental Europe the torso is measured in centimetres and rounded to the nearest multiple of 5 cm. Band sizes run 65-70-75-80…, increasing in steps of 5 cm, similar to the English double inch. A person with a loosely measured underbust circumference of 78–82 cm should wear a band size 80.
The cup labels begin with "AA" for an 11±1 cm difference between bust and underbust circumference, i.e. not between bust circumference and band size as in the English systems. They increase in steps of 2 cm, instead of 2.5 cm or 1-inch, and except for the initial cup size letters are neither doubled nor skipped. In very large cup sizes this causes smaller cups than their English counterparts.
This system has been standardized in the European dress size standard EN 13402 introduced in 2006, but was in use in many European countries before that date.
In South Korea and Japan the torso is measured in centimetres and rounded to the nearest multiple of 5 cm. Band sizes run 65-70-75-80…, increasing in steps of 5 cm, similar to the English double inch. A person with a loosely measured underbust circumference of 78–82 cm should wear a band size 80.
The cup labels begin with "AAA" for an 5±1.25 cm difference between bust and underbust circumference, i.e. similar bust circumference and band size as in the English systems. They increase in steps of 2.5 cm, and except for the initial cup size letters are neither doubled nor skipped.
Japanese sizes are the same as Korean ones, but the cup labels begin with "AA" for a 7.5±1.25 cm difference and usually precedes the bust designation, i.e. "B75" instead of "75B".
This system has been standardized in the Korea dress size standard KS K9404 introduced in 1999 and in Japan dress size standard JIS L4006 introduced in 1998.
The French and Spanish system is a permutation of the Continental European sizing system. While cup sizes are the same, band sizes are exactly 15 cm larger than the European band size.
The Italian band size uses small consecutive integers instead of the underbust circumference rounded to the nearest multiple of 5 cm. Since it starts with size 0 for European size 60, the conversion consists of a division by 5 and then a subtraction of 12. The size designations are often given in Roman numerals.
Cup sizes have traditionally used a step size of 2.5 cm, which is close to the English inch of 2.54 cm, and featured some double letters for large cups, but in recent years some Italian manufacturers have switched over to the European 2-cm system.
Here is a conversion table for bra sizes in Italy with respect other countries:
Advertising and retail influence
Manufacturers' marketing and advertising often appeals to fashion and image over fit, comfort, and function. Since about 1994, manufacturers have re-focused their advertising, moving from advertising functional brassieres that emphasize support and foundation, to selling lingerie that emphasize fashion while sacrificing basic fit and function, like linings under scratchy lace.
Women with larger breasts (cup size greater than D) can have a difficult time finding a correctly sized bra because many stores do not offer a sufficient range of bras in greater sizes. Many salespeople are not trained in how to properly fit a bra, and when the customer can not find what they want, will sell the customer the next largest or smallest size. Some salespeople measure customers over their shirt and bra, adding errors to every measurement. Elisabeth Squires, an author of a breast-health and bra guide, says "Most really good fitters will tell you this is an art, not a science."
English mechanical engineer and professor John Tyrer from Loughborough University tackled the problem of bra design after his wife returned disheartened from a shopping trip when she could not find anything to suit her needs. On assignment from the British government, he uncovered that 80% of women wear the wrong size of bra. He reported that women are measuring their chest diameter and maximum breast diameter rather than their breast volume, especially when the body is in motion. According to Tyrer, "to get the most supportive and fitted bra it's infinitely better if you know the volume of the breast and the size of the back.". He says the A, B, C, D cup measurement system is flawed. "It's like measuring a motor car by the diameter of the gas cap." "The whole design is fundamentally flawed. It's an instrument of torture." Tyrer has developed a bra design with crossed straps in the back. These use the weight of one breast to lift the other using counterbalance. Standard designs constrict chest movement during breathing. One of the tools used in the development of Tyrer's design has been a projective differential shape body analyzer for 40,000 GBP.
Contrary to popular belief, breasts weigh up to ~1 kg and not ~0.2 .. 0.3 kg. Tyrer said, "By measuring the diameter of the chest and breasts current measurements are supposed to tell you something about the size and volume of each breast, but in fact it doesn't". Bra companies remain reluctant to manufacture Tyrer's prototype, which is a front closing bra with more vertical orientation and adjustable cups.
Calculating cup volume and breast weight
The average breast weighs about 0.5 kilograms (1.1 lb). Each breast contributes to about 4–5% of the body fat. The density of fatty tissue is more or less equal to 0.9 kg/l for all women.
If a cup is a hemisphere, its volume V is given by the following formula:
where r is the radius of the cup, and D is its diameter.
If the cup is an hemi-ellipsoid, its volume is given by the formula :
where a, b and c are the three semi-axes of the hemi-ellipsoid, and cw cd and wl are respectively the cup width, the cup depth and the length of the wire.
Cups give a hemi-spherical shape to breasts and underwires give shape to cups. So the curvature radius of the underwire is the key parameter to determine volume and weight of the breast. The same underwires are used for the cups of sizes 36A, 34B, 32C, 30D etc. ... so those cups have the same volume. The reference numbers of underwire sizes are based on a B cup bra, for example underwire size 32 is for 32B cup (and 34A, 30C...). An underwire size 30 width has a curvature diameter of 3-inch 5/6 ≈ 9.7 cm and this diameter increases by ⅓ inch ≈ 0.847 cm by size. The table below shows volume calculations for some cups that can be found in a ready-to-wear large size shop.