Brassiere

Measurement systems

Although all bras are labeled by size, many women find that the only way to obtain a bra that fits properly and achieves the effect they want is by trial and error with each bra type, model and brand. This method is the most reliable.

Though many countries use the metric system (centimetre) to measure things typically measured in the customary system (inch), the majority of these nations still use inches to determine the underband size of the bra itself.

There are several methods which may be used to provide an approximate size by taking measurements. However, bra sizing systems differ widely between countries, between manufacturers, and between brands and designs, which can create manyproblems. Many researchers have demonstrated that these problems arise because fit requires knowing the breast volume, not the body circumference (the distance around the body), which is what is actually measured. Although bra sizing uses the circumference to estimate the volume, this has been shown to be highly unreliable.

The size of a bra is commonly described by two values. The first is the band size (underband), a number based on the circumference of the chest under the bust, excluding the breasts. The second is the cup size given by a letter of the alphabet, and relating to the volume of the breasts themselves. For example, a 30D bra is for a 30-size band and a D-size cup. Cup sizes typically start with A, the smallest, and increase alphabetically. While there is some general agreement about the meaning of A-D, which includes the vast majority of women, cup sizes greater than D become increasingly unreliable. A double lettering system may also be used, e.g. DDD for F or AA for a size smaller than A.

Band size is usually determined by measuring body circumference either under or above the breasts and then adding a specified amount to account for the fact that the ribcage is generally wider at the height of the breasts than at the point at which one measures. A second measurement is then taken of the chest circumference over the fullest part of the breasts (overbust). The cup size can then be calculated with tables or a conversion tool from the difference between these two measurements.

A common mistake is to take the overbust measurement with a bra on, instead of braless, with the breasts held at the desired position. The mean underband circumference in the UK is 34 inches (86 cm). For the overbust measurement, this is 40 inches (101 cm), for women 18–64 years.