Breast measurement
Breast measurement involves the measurement of the breasts for quantifying physical characteristics such as size, shape, and developmental state. A variety of different approaches have been employed for measuring the breasts.

Tanner staging

Tanner staging can be used to assess the developmental state of the breasts during puberty, from childhood (Tanner stage 1) to adulthood (Tanner stage 5).

Breast volume
Breast volume is a method of measuring the size of the breasts. A variety of techniques have been used to measure breast volume, including water displacement, plaster casting, medical imaging (e.g., mammography, magnetic resonance imaging (MRI), ultrasound), and 3D scanning. There is substantial measurement error with many breast volume measures, but MRI imaging appears to have among the lowest error and hence to be the most accurate measure. However, 3D scanning might have the potential to become the new gold standard for clinical assessment.

In a normative study of breast volumes in women using 3D scanning, breast volumes were median 515mL, mean 650mL, interquartile range 310 to 850mL, and range ~50 to 3,100mL. In transgender women, breast volume measured with 3D scanning has been reported to reach a plateau of around 100mL (but with an apparent range of up to 750mL) after 3 to 4years of hormone therapy.

Breast circumference

Breast circumference, also known as bust circumference, is a measurement of the circumference of the torso at the level of the breasts. It has been used as a measure of breast size in normal young women, in women with pregnancy, and in transgender women. Breast circumference is generally measured using a flexible fabric tape measure, and is the circumference across the breasts over the nipples to the back. The breast–chest difference is breast circumference minus band or underbust circumference and is used in the determination of bra cup size.

Breast–chest difference

Breast–chest difference, also known as bust–band difference, is a measurement used for quantifying breast size. It is calculated as bust circumference minus the band or underbust circumference. Breast–chest difference has been used in the measurement of breast development in transgender women on feminizing hormone therapy.

Bra size

Bra size, also bra cup size, is a measurement of the breasts for selecting bras, taking into account breast size and torso circumference. It is determined using the breast–chest difference, with 12–14cm equating to an A cup, 14–16cm a B cup, 16–18cm a C cup, and 18–20cm a D cup.

Breast hemicircumference

Breast hemicircumference, also sometimes referred to as breast width or as breast circumference (incorrectly), is an anthropometric measure of the breasts which has been used in studies to assess breast development and breast size, including in transgender women. It is the medial horizontal length (measured with a flexible tape measure) from one side of the breast to the other side and running over the nipple. A measurement of 7inches is said to correspond to an A cup, 8inches to a B cup, 9inches to a C cup, and so on, with each further 1-cm increment or decrement corresponding to one cup size up or down.

Breast unit
The breast unit is a measurement of the breasts in which the breasts are measured horizontally and vertically and then these values are multiplied to given an overall idea of breast size. It was devised by Vincent J. Capraro and has been used in pediatric endocrinology to quantify breast development. The method has been described as follows:

The breast unit has also been used to quantify breast size in girls and women with complete androgen insensitivity syndrome (CAIS) and other individuals with disorders of sexual development.

References

Anthropometry
Breast