A bra size consists of a number paired with a capital letter; the number references a band size, to fit the ribcage, and the letter references a cup size, to accommodate the breast mound. While this labeling protocol is globally consistent, the number and letter combinations vary between countries and even manufacturers within countries making it difficult to understand reasoning behind bra sizing. Two key factors lie at the root of global bra size confusion; LABELING PROTOCOLS and GRADE VARIANCE . The Bra Size Calculator page can suggest global equivalent bra sizes.
LABELING PROTOCOLS for bras vary between manufacturers and countries partly because the grade variance produces different base measurements and partly because manufacturers use different methodologies to assign band size. The following diagram illustrates the seven main methods used for labelling bra bands. Note that there are different underbust girth measurements associated with band labels.
The GRADE VARIANCE (difference between sizes) varies between countries. The Industry Breast Parameters page explains grade variance but basically countries use either 4cm (1.57 inch) or 5cm (2 inch) girth difference between sizes. Note that the 4cm (1.57 inch) key grade system produces more band options than the 5cm (2 inch) system. The green rows illustrate bands that reflect the same underbust measurement. All other bands vary in the underbust girth between countries making it confusing to decipher between global band sizes.
**NOTE** These charts were last updated on April 16. At that time a minor error with regards to cup sizes over a “Q” was noted and fixed. If you viewed these charts prior to this date they may have contained minor errors. Every attempt is being made to keep data on this website accurate.
Cup Size refers to the volume capacity of a bra cup. To further complicate bra sizing, the same cup letter may reference different volumes in different countries. The following diagram illustrates globally equivalent cup sizes. The standard method for calculating these cup sizes is to subtract the underbust girth from the bust girth. The resulting number is referred to as a cup indicator. The Bra Sizing Myths page explains why using a cup indicator (the difference between the bust and underbust or highbust girth) is an inaccurate gauge of cup size. In general an accurate cup size can not be configured from girth measurements. Cup size can only accurately be configured from direct measurement of the breast mound as detailed on the Bra Size Calculator page. Occasionally the direct measure of the breast mound and the cup indicator will produce the same cup size but this is not always so. This is because some bras are designed to minimize bust girths while others are designed to enhance it. The yellow rows illustrate cups that reflect the same overbreast measurement. All other cups vary in the overbreast measurement making it confusing to decipher between global cup sizes.