Step 1, Measure for Band Size:
Need help? Expanded band measuring instructions.

Keeping the measuring tape parallel with the ground, 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. Round all fractional measurements to the nearest whole number.

If the measurement is even, add 4"
if the measurement is odd, add 5"


Step 2, Measure for Cup Size:
Need help? Expanded cup measuring instructions.

Standing straight, with your arms at your side, measure at the fullest part of your bust (while wearing a non-padded bra) making sure the measuring tape is parallel with the ground and not binding.

Round all fractional measurements to the nearest whole number.


Step 3, Calculate Your Bra Size:

Subtract your band measurement (step 1) from your cup measurement (step 2). Generally, for each inch in difference, the cup goes up by one size. See the conversion chart here.

Example:
Step 1: 34" under measurement +4" = 38" band
Step 2: 40" over measurement
Step 3: 40" - 38" = 2" or Cup "B"
Your size would be 38B