There are many great resources out there to helping you figure out your bra size – A Bra That Fits is one of them!
But here’s a quick-and-dirty method for figuring out your “starting point” bra size:
1. Get a fabric tape measure.
2. Take a firm measurement of your underbust (i.e. your ribcage right under your breasts, without wearing a bra so the band won’t get in the way).
Write this number down. This is your approximate band size.*
3. Take a fairly loose standing bust measurement. The main goal here is to measure how much breast tissue you have, so measuring while wearing a bra that squishes you down isn’t going to be helpful or accurate. Then, for better accuracy, take another bust measurement while bending forward at the waist.
Write these numbers down. If there is a large difference between them, start with the average.
4. Subtract the number you got in Step 2 from the number(s) you got in Step 3. The resulting number indicates approximate cup size, using 1 inch per cup letter (i.e. 4 inch difference = D cup, 5 inch = DD, etc). Use this U.S. vs U.K. Size Chart to help you determine the correct cup size (starting at A=1). The majority of good, well-known bra companies use UK sizing.
An example:
Underbust measurement: 28 (band size)
Standing bust measurement: 34
Leaning bust measurement: 35
34-28 = 6 inch difference (A, B, C, D, DD, E)
Bra size: 28E or possibly 28F
*note: if you get an odd number (like 33), you’ll need to round to the nearest even number for your band size – generally it’s best to round down, but experiment with both 32’s and 34’s (in this case).
Exceptions to the “rules”:
-Women who are more muscular and have “flared ribcages” may need to go up a band size or so from what their underbust measurement indicates, especially if they have smaller breasts.
-Women who have larger underbust measurements and/or more cushion around their ribcages may well be able to go down several band sizes from their underbust measurement, as bands get stretchier as they get larger (a woman with a 39″ ribcage, for example, may possibly do best with a 36 band)
-Women with little cushion around their rib cage (“bony ribcage”), often paired with a small underbust measurement, may need to go up in band size for comfort.
-Cup size may vary a bit based on breast shape.
-Remember that this gives a starting point size only. Bra fitting is an art, not a science, and you’ll probably have to try on several things to get the best idea of what size and shape works for you. Do your research, and go with the bra and size that fits and feels the best!