BCD sizing is a sizing method developed by Beverly Johnson in the 1990s. It is much more reliable and easier to use than the traditional ABC sizing you find in ready-to-wear. The BCD, is simply the Bottom Cup Depth measurement of the breast. That is the distance, in inches, from the apex in a supported position to the base of the breast along the infra-mammary crease (known as the wire line)
In the BCD system, all cup sizes increase or decrease by ¼”; each size will accept 3 different wire sizes and each BCD size includes 5 band sizes. So each BCD size is equivalent to 5 ready-to-wear bra sizes, even the ones in between two sizes. If you need one size larger (or smaller), just go up (or down) one BCD size. No more confusing “sister sizing” to figure out!
There are several ways to measure for your BCD size :
use a flexible tape measure and measure the distance while not wearing a bra and while standing – from the apex to the wire line. If your breast tissue is soft, you can lean over so your back is parallel to the floor and measure again. The average of the two measurements is your BCD.
if you have a ready-to-wear bra that fits and it has a seam across the apex, you can measure from the wire up to the seamline. This is a very common way to get started.
if you have sewn a bra that fits, you can measure from the notch at the base of the breast (if there is one) up to the cross cup seam, on the lower cup pattern piece. See the drawing below. Once you have sewn a bra using the BCD size system, every bra you make that uses that system should fit you. This is much better than the trial and error you might go through with an untested pattern.
Refer to the helpful BCD size chart at the end of this post. Find your ready-to-wear size in the first column, and its BCD size equivalent is in the second column. The third column is useful for confirming the wire sizes that fit this particular BCD. Each BCD size includes 5 band sizes, even ones that are usually “in between” and therefore have to rely on sister sizing.
To find your band size , measure your rib cage around in inches, once while fully inhaled and again after exhaling. The average of the two numbers is your band size. If you have measured in centimeters, divide the answer by 2.54 and round to the nearest full number. For example if you measure 86 cm, divide by 2.54, which gives you 33.8″. You would use 34 as your band size as it is the closest whole number.
