BCD size? 4 ways to measure it

What is a BCD size, anyway? The BCD is a sizing method developed by Beverly Johnson, (known as your Fairy Bra Mother) in the 1990s to solve the challenge of ready-to-wear bra sizing and its many variables when measuring. Different companies use different algorithms to determine their cup sizes, and brands from other countries may not follow the same guidelines at all.

Some brands use the difference between a high bust measurement and the full bust to find the cup size, while others have you measure the rib cage, add either 3 or 5″ to that measurement, and subtract that new number from the full bust measurement to determine the cup size. Still others, use your rib cage measurement as is and subtract that from the full bust measurement to find the cup size. the problem with ALL of these methods is that they are using your back width as part of that measurement. that means if your back is wide (or narrow) you will end up with a very different cup size than you really are.

There is a better way

Your BCD size 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, sometimes 4 different wire sizes and each BCD includes 5 band sizes. So each BCD 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!

4 ways to measure 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. Each pattern I’ve created for Beverly Johnson Designs has five band sizes that correspond with each BCD, and it is very easy to make the band larger or smaller if it needs to be.

Below is a chart I have made for all the class patterns in my new line, Beverly Johnson Designs. As you can see, the new line has 63 Ready-to-wear bra sizes listed, but only 15 BCD sizes! That’s because the the BCD system has the ability to fit by measuring a real part of the body, and not one that could be affected by other areas.

For help with fitting challenges, or sewing issues, we are here to help in my private Facebook group, Beverly Johnson’s Bra-making Support group. We would love to have you as a member!