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By Asa Salas

Bra sizes are made up of two components: An even number that represents the band size (32, 34, 36, etc.), and a letter that indicates the cup size (A, B, C, etc.) determined by the size of the breast itself.

There are many competing methods for determining the best bra size to select. What follows is the method with which we have had the most success.

Always measure while wearing your own best fitting bra - This should NOT be a sports bra, but rather a "lingerie" style bra, as you would typically wear underneath a blouse.

To determine the band size:
Measure snugly around your ribcage, directly under your breasts. Add 3 inches to this measurement. For example, if your ribcage is 31 inches, your band size is 34. If your result is an odd number, go UP to the next band size.. For example, if your rib cage is 32 inches, 32+3=35, round 35 up to a 36 band size.

To determine the cup size:
Measure loosely around the fullest part of your bust. Subtract the band size from this measurement. Use this number to determine your cup size according to the table below.

Difference 0″ 1″ 2″ 3″ 4″ 5″ 6″
Cup size AA A B C D DD/E DDD/F

Example: if your ribcage measurement is 31, and your bust measurement is 37, your bra size is a 34C: 31+3=34, so 34 is your band size. Since 37-34= 3, you've got a C cup.

Fitting hints:

  • If the band size comes out to an uneven number, try the next band size up.
  • If you are in-between sizes or you are having difficulty finding the correct fit, then try this this method: Go up in cup size and come down in band size OR Go up in band size come down in cup size. For example, if you are wearing a 42D, but it is a little too snug around the band, try moving up to a 44 and down to a C.
  • If your breasts are two different sizes, try to fit the smaller breast.

Fit Check List:

  • First and foremost: Does the bra feel comfortable?
  • Is the bra snug around your body without being too tight?
  • Do the cups completely contain your breasts?
  • If breasts spill over the top or sides of the cup, the cup is likely too small.
  • If there are gaps or puckering in the cup, the cup is likely too large.
  • Does the back of the bra stay in place? If it rides up, you may need a smaller band size.
  • Does the center of the bra stay flat against your breastbone? If not, the cups may be too small.
  • Do the straps support your breasts without digging into your shoulders? If not, you may need a bra with wider straps, or more structure in the band and cup to relieve pressure on the strap.


Compression uses elastic support fabrics to hold breasts closer to the body. Reduces the amount of bounce, but may produce a “uniboob” appearance which some women object to.

Encapsulation is another method of reducing bounce, encapsulation typically uses molded, often semi-rigid cups to contain the breasts. The shape of the cup, and the way it's built into the bra, limits movement of the breasts.

Many bras use a combination of compression and encapsulation to support breasts.

Underwire/frame support system
Stiffening components underneath the breast hold it up and provide shaping. May also contribute to the overall support of the bra.

Straps support the weight of the breasts by cantilevering it off the shoulders, much like a suspension bridge. Larger breasts require broader, non-stretchy straps.

Many A/B bras are designed to pull over the breasts. When there's a lot of difference between band size and bust size, it's difficult to pull on a bra that's suitably sized in the band, so most C/D/DD bras have a front or rear closure. To prevent chafing, the closure should be covered so that it's invisible to the skin.

Asa Salas is an expert-ranked cross country and DH mountain bike racer. Her sponsors include Independent Fabrication, Truvativ, Suga Clothing, Velocity Gear and Cycle Path. She is also an avid road cyclist. Asa has worked as a mechanic at "The Bike Shop" in Fair Oaks, California for six years, and has been training and riding competitively for eight.