Measuring Bust Size for a Sports Bra
Stand in front of a mirror, wearing an unpadded bra and no shirt.
Use the tape measure to determine the size of your chest. Make sure the tape is snugly -- but not tightly -- wrapped just under your arms and above your breasts. This measurement is the standard number part of your bra size, for example, 36". You should round down to the nearest inch.
Place the tape measure around your breasts at the fullest part of your bust and record the number, for example, 38". This will enable you to find your cup measurement. Subtract your chest number from this bust number. If the difference is less than an inch, the cup size is AA. One inch equals A, two inches is B, three means a C, four inches for D and five inches represents DD. For our example: 38"-36"=2", making the cup a size B.
Put the two numbers together to come up with the bra size; for example, 36B. Now, translate that into sports bra sizes. A size small sports bra fits busts in the 32-34 A/B range while a medium is made for sizes 34-36 B/C. Chests measuring 36-38 C will need a size large sports bra and an XL bra will cover 38-40 C/D.
Try on the bra if shopping in person to ensure a proper fit. The sports bra should be snug but not too tight across your chest. If it is uncomfortably tight, you need a larger sports bra.