A bra size is made up of two measurement components: band size (i.e. 34, 36, 38) and cup size (i.e. A, B, C).
To find your correct bra size, begin by wearing your best fitting bra - unpadded, and not a minimizer or sports bra (underwire doesn't matter). If you are sagging in this bra, tighten your straps until the crest of your breasts is approximately half way between your shoulder and your elbow - this is the proper alignment for most breasts. If possible, have someone other than yourself take your measurements. Not only is it faster, it also tends to be more accurate. (Download a Printable Tape Measure here.)
Measuring Your Band Size
1. Holding the measuring tape gently but firmly, measure around your bra directly under your bust after expelling all air from your lungs - you want this measurement to be as small as possible. Look in a mirror to assure the tape is parallel to the floor. The position of your tape measure is critical here. If you have the tape too high, your measurement will be too large; too low and it's too small.
2. When you take these measurements, round to the closest whole inch, either up or down. For example, if your measurement is 29 3/8", round to 29". If your measurement is 29 1/2" or more, round to 30".
3. Bras come in even band sizes. If the rounded measurement you come up with is an even number, add 4 inches. If the rounded measurement you come up with is an odd number, add 5 inches.
4. The result is your band size. Example: 33" + 5" = 38" band size
Another method for finding your band size is to measure around your body, straight across your back and chest directly above the bust at underarm level. Again, expel all your air, stand up straight, and keep your arms at your side. High-busted women and women with implants will have trouble keeping the tape measure parallel to the floor; do your best. If this measurement is an odd number, add one inch and the result will be your band size.
Measuring Your Cup Size