Step One: With a fabric tape, measure under your arms above your bust. Round your measurement number up to the nearest even number.
This number represents your band measurement.
Step Two: with a fabric tape, measure under your arms around the fullest part of your bust. Keep the tape level across your back.
Step Three: Subtract the difference between your band measurement from your chest measurement.
Example: If your above chest measurement is 33.5", round to 34". Now measure across your chest. If that measurement is 37 1/4", you subtract 37-34=3". Your bust difference is 3 inches.Your size is 34C.