i've heard that they do it, but i got one done at nordstroms about a year ago, it was worth it, you have to make an appt. And the bra i bought didn't cost that much than the ones in vs but i was wearing the wrong size AND style.
I pulled this off the internet:
Step 1
While wearing your best fitting non padded bra measure tightly around your rib cage just beneath your bust line. Add 3 to 5 inches to this number to determine your approximate band size.
Step 2
Double check your band measurement by bring the tape measure tightly around your ribcage just above your bustline. This second measurement should be the same as your calculated band size from step 1.
Step 3
Measure loosely around the fullest part of your bust or where the fullest part of your bust should be (usually lined up with the nipple about halfway between your shoulder and your elbow). Subtract your band size from this number. Generally, each inch of difference equals one cup size:
Cup Size Inches Of Difference
AA 0-.5"
A .5-1"
B 1-2"
C 2-3"
D 3-4"
After the A,B,C,D things get a little tricky. Some companies offer D, DD, DDD only, some equate the DD with an E and still others offer DD and E as separate sizes.
Keep in mind that there is a lot of rounding and estimating involved and every brand has their own standards.
The cup size is always in proportion to the band size (A 32D has the same size underwire -ie cup size- as a 34C or 36B). If you measure yourself as a 34G you might also try a 32GG or a 36H for the same amount of underwire.
Cup size is actually the combination of the width of the underwire and the depth of the cup. Some bras like some breasts are wide but not deep or deep but narrow and there are different designs for different shapes of breast. This is why some styles fit some sizes that other styles may not.