Step 1:  Find your bra band size

​Wearing an unlined, non-padded bra or fitted t-shirt, run the measuring tape all the way around your back where your band sits, being careful to keep the tape level. Take a couple if deep breaths and make sure the band isn't too tight. You should be able to comfortably fit two fingers beneath the tape measure. If you don't get a whole number (e.g. 38 and 1/2 inches), or you get an odd number that's between traditional band sizes (e.g. 38 inches), round up to the nearest whole, even number (39 inches). That number is your bra band size.

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Step 2: Measure your bust 

​To measure your bust, "run the measuring tape around your back, just under your shoulder blades, and up around the fullest part of your bust. The tape should just skim the bra in front."

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Step 3: Calculate to find your cup size

​Subtract your band size from your bust measurement to find your cup size. The difference in inches correspond to your cup size. For example, if your bust measures 39 inches, and your band is 36, the difference will be 3. On the chart to the left, you'll see a 3 is equal to a C cup, measuring 36C.