Traditional bra sizing consists of two measurements, the BAND size (chest size), and the CUP size (breast size). Both band size and cup size derive from measurements, but are not themselves measurements.
What is my band size?
Band sizes are only EVEN NUMBERS, and are determined by adding 4, 5, or 6 to the “underbust” or rib cage measurement. A tape measure wrapped snugly around the entire chest just beneath the bottom of your breasts in inches is your starting number. If the number is even, add four or six and if the number is odd, add five to learn your band size. Your band size is not the bra measurement, because an elastic bra stretches more than non elastic. A band size 36 elastic bra may measure 27 inches in length while a less elastic size 36 bra may measure 33 inches in length.
What is my cup size?
Cup size is determined by the relationship between measurement around your breasts (bust size) with the measurement below (or above) your breasts. Bust measurement two to four inches larger than chest measurement is usually an A cup, three to five inches larger is a B cup, four to six inches larger is a C cup, five to seven inches larger a D cup, and so on. You can see there are ranges and overlap, and cup size also depends on bra style and pattern. Many cup sizing schemes are inaccurate for some women, partly because of the wide range of breast shapes and variety of bra types and fabrics. Dr. Edward Pechter, a plastic surgeon, determined cup size accurately by direct measurement across the breast.
For women with a 36 band size, the breast measuring 7 inches wide across its fullest part from the lateral origin beneath the arm to its inner termination near the sternum is an A cup, 8 inches a B cup, 9 inches a C cup, and so forth. Adjusting for the fact that cup size varies with band size (the C cup of a 36 bra is larger than the C cup of a 34 bra but not as large as the C cup of a 38 bra), one half inch is added to or subtracted from breast measurement for each band size up or down. For example, if a breast width of 9 inches is a C cup for 36 band size, a breast width of 8.5 inches is a C cup for 34 band size and breast width of 9.5 inches is necessary to fill a C cup for a woman with 38 band size.
Conventional Bra Size Chart:
Pechter Method for Determining Bra Size and Predicting Post-Augmentation Breast Size:
The Pechter Method determines bra cup size by direct measurement of the breast.
For a 36 band size, a breast circumference from outside crease to inside termination of the breast across the meridian of greatest circumference (usually across the nipple) of 7 inches corresponds to an A cup, 8 inches a B cup, 9 inches a C cup, 10 inches a D cup, !! inches a DD cup, and 12 inches an E cup. In Dr. Edward Pechter’s original study of 100 women subjects, his technique for cup sizing agreed with the woman’s own estimation of her cup size 84% of the time and the traditional method (above) of bra measurement agreed with each subject’s estimation only 23% of the time.
Bra size is determined by two measurements, Band size and Cup Size.
Band size is expressed as a number, whereas cup size is represented by a letter (A,B,C,etc.). The conventional method of determining cup size does not rely on the direct measurement of the breasts but instead relates the circumference of the chest immediately below the breasts to the circumference of the chest around the fullest part of the breasts. In the most common method of bra sizing, band measurement is determined by wrapping a tape snugly around the chest immediately below the breasts. Five inches is then added to that number. If the number is odd, it’s rounded off to the next highest even number (because bras are only offered in even numbered sizes).
For example, if the under-bust chest circumference is 29 inches, the band size is 34 (29 + 5). If the underbust chest circumference is 32 inches, the band size is 38 (32+5=37, rounded up to the nearest even number=38).
The bust circumference is determined by measuring the distance around the chest loosely with a tape across the fullest part of the breasts, usually at the level of the nipples, with the woman wearing a non-padded bra. Cup size is then calculated by the difference between bust circumference to underbust plus five measurements.
A difference of 3 inches equals an A cup, 4 inches a B cup, 5 inches a C cup, 6 inches a D cup, and so forth. For example, a woman with a bust circumference of 38 inches and a band size of 34 (underbust chest circumference of 29 inches + 5 inches) would be a B cup (38-34=4-inch difference =B cup).
Dr. Pechter’s study measured bra cup size by the traditional means and compared with measurements directly across each breast. This measure was horizontal distance across the skin of each unclothed breast with a tape from the lateral (outer) breast crease to the medial (inner) breast crease.
For women with a band size of 36, a measurement of 7 inches corresponds to an A cup, 8 inches a B cup, 9 inches a C cup, etc., with each one-inch increment determining a cup size up or down. For every change in band size up two or down two, the cup size measurement in inches increases or decreases one-half inch respectively.
Thus, a woman with 34 band size will be a C cup if the measurement across her breast is 8.5 inches. In small or firm breasts, the circumference can simply be measured in the standing position. Women with large or sagging breasts are more accurately measured in the supine position (laying on back).
The point where the breast mound begins laterally can sometimes be more easily discerned with the woman’s arms elevated. Gently pushing the breast laterally to the outside or medially toward the inside may help define the breast creases for accurate measurement.
The video below demonstrates a clear demarcation of medial (inner) breast margin (crease) when she pushes upward and slightly inward on breasts. The same pressure on the breast defines outer (lateral) breast crease. It is from the inner to the outer crease that measurement in inches most accurately determines the correct cup size, as described above.
In his study of 100 women, Pechter’s method was accurate for over 80% of women, and never off by more than one cup size. Traditional cup sizing methods provided results that were smaller than those stated by women subjects, often by two or more cup sizes.