Bustyresources Wiki

Using the accurate method, one will use only these two measurements and not add any inches.

Many bra-fitting methods exist and are practiced by both individuals and retailers. However, not all are equal, or will produce the best fit for the one measured.

Bra sizes can vary wildly from true size based on method followed. Thus, using a reliable method is incredibly important to yield a good size as a starting point.

However, none of these methods produces a "true" bra size; just bra sizes of varying degrees of closeness to one's actual fit. It is vital to try on bras in person and evaluate fit based on each individual bra, regardless of labelled size. This becomes especially important after taking into account sizing differences between manufacturers, as well as countries.

Accurate method[]

Main article: How-to determine bra size

Most simply put, by this method, one finds the underbust measurement; this becomes the band size (if odd, then round to preferred even number: smaller for tightness, larger for looseness; adjust based on fit). The cup size is then calculated by finding the bust measurement, then subtracting the band size from the bust measurement. For each increasing inch of difference, the cup size increases by one. A bra is not worn while taking these measurements to allow for true breast size.

A woman measures herself (while not wearing a bra), and finds that her underbust measures 31 inches and her bust measures 39 inches. By this method, she opts for a size 32 band. To find her cup size, she determines that . She finds a bra size of 32F (UK sizing) or 32DDDD/F/G (US sizing; varies by manufacturer).

Inaccurate methods[]

There are several bra-fitting methods retailers and manufacturers use on customers that will produce a bra size far away from the wearer's ideal size(s). Most of these inaccurate methods will result in a band too large and cups that are too small.

Size lines

The three common breast measurements: underbust (A), bust (B), chest (C).

Underbust plus inches[]

Some guides or fitters advise finding one's underbust measurement (line A), then adding 4" if it's an even number or 5" if it's an odd number. This number becomes one's band size. From there, the cup size is calculated by subtracting the bust measurement (line B) from this band size, and for every inch difference, the cup size increases by a letter.

The woman in the previous example found that her underbust was 31, and her bust was 39. By this method, she should add 5" to her underbust measurement, yielding a band size of 36. Her cup size becomes the difference between her bust and underbust, , corresponding with a cup size of C. Thus, her bra size by this method is 36C (in both US and UK sizing).

Above bust as band size[]

Another common fitting method consists of measuring above the bust, called "overbust", essentially in the armpits (line C). If odd, add one. This measurement is then taken as the band size. Cup size is measured as the difference between this band size and the bust measurement. However, this measured band size will most likely to be inaccurate, based on differences in body shape (broader shoulders yield a too larger number, a larger rib cage means a too small number, etc.).

The same woman as in previous examples finds that her above bust measurement is 33 inches. Adding one, she has a band size of 34. Using a her bust measurement of 39, she yields a bra size of 34DD by this method (in both US and UK sizing).



The diagonal method is described in measurement guide.[1]

In this method, most notably used by Victoria's Secret, one holds the tape at band level in the back, then angles the tape upwards and diagonally to above the bust. If odd, subtract one. This number is the band size. The cup size is based on the difference between the bust and band size.

The same woman as in previous examples finds that her diagonal measurement is 37 inches. She subtracts one to obtain 36. Using the bust measurement of 39, she yields a bra size of 36C (in both US and UK sizing).

While wearing a bra[]

By this method, an individual calculates the band size using any of the previously mentioned methods. However, the individual wears a bra while measuring the bust. Depending on the fit of this bra, the bust measurement may run larger (if the bra is too large) or smaller (if the bra is too small) than its true value.

Let's assume that in all previous examples, the same woman was not wearing a bra while measuring herself. But in this case, she is wearing a too-small bra when measuring bust, and obtains a measurement of 37. Assuming she uses her true band size of 32, her final bra size by this method is 32DD (in both US and UK sizing).

Other breast measurements[]


Plastic surgeons have adopted a method for measuring breasts that is totally unrelated to bra size. This method is used to determine individual breast size for surgical purposes, such a reduction or augmentation.

In this method, a tape measure starts at the outside of the chest, under the arm (where the breast begins). It is drawn across the fullest portion of the breast (typically over the nipple), then, it ends at the breast bone (where the breast ends). Based on this length, a "cup size" is assigned to each individual breast.[2]

Length to cup size conversion
Measurement Cup size
Inches Centimeters
7.0 17.8 A
7.5 19.0 Full A
8.0 20.3 B
8.5 21.6 Full B
9.0 22.9 C
9.5 24.1 Full C
10.0 25.4 D
10.5 26.7 Full D
11.0 30 DD


There is no wholly accurate way to measure the amount of fat tissue in one's breasts,[3] but there are several ways to get a general idea of their weight,[4] like water displacement.[5][6]

Without Tape Measure[]

Using a tape measure is not the key to getting a great bra fit – they’re not necessary and many fully trained professional fitters don’t use them. Below are guidelines on how to ensure you select the best fitting bra.

Step 1: Finding the correct back size[]

The back size of a bra is about how the bra fits your body. This part provides most of the support, so it is important that it is firm, but also comfortable.

The band of your bra should aligned horizontally, and should never ride up your back. If the band is loose or rides up, try a smaller size. When decreasing your band size remember to increase your cup size as appropriate.

Over time, bras will stretch, so when buying a new bra, make sure it fits on the loosest hook, allowing you to move inwards as the band wears.

Step 2: Finding the correct cup size[]

In the same way that the band size is about how a bra fits the body, the cup is about the volume of your boobs. Always ensure the front wires of the bra are flat against the breast bone. You should also ensure that your boobs are completely covered by the cups, and that there is a smooth line between the top of the cup and the top of your boobs.

If your boobs bulge at the top, or the wires aren't flat, opt for a larger cup size. Alternatively, if you have spare room, try a smaller size.[7]