"Sister sizes" are bra sizes that have the same cup volume, but a different band size.
This is possible because band measurements are consistent across sizes (a 10D has the same band fit as a 10J), but cup volumes are not. A "DD" cup isn't a fixed measurement. An 8DD is a completely different cup size than a 16DD!
THE CHART
(pinch to zoom on mobile)
HOW TO USE THE CHART
All of the sizes in the same horizontal row have the same cup volume, just different band sizes.
Here are a few common scenarios for sister sizing:
I THINK MY BAND IS TOO BIG
If you watched our video here and learned that your band size is probably too big, you're in good company. Most women are wearing bands too big!
If your cups fit well, simply try the size directly to the left of your current size on the chart. So if you've been wearing a 14DD but suspect your band is too big, try a 12E for the same cup volume.
MY USUAL SIZE IS SOLD OUT
Sister sizing to the rescue!
If you get a good fit in a size that's sold out, you could try ordering the size directly to the right of your usual size on the chart.
This will be one band size bigger, but have the same cup fit as your normal size. You can get away with this in our adjustable back bikini styles, because you can bring the back in to fit. Wearing a band size too large in bras isn't advisable, and will work best if your usual band size is quite a snug fit.
Of course, it's not ideal to be wearing a band size larger than normal, but it will work in a pinch!
I WANT A ONE PIECE, but I'm a different size on top and bottom
Great news, we have a dedicated one piece size chart available here!
To find your one piece size yourself, simply find the size in your sister row that corresponds to your pants size.
For example, if you usually wear a 10HH bra and a size 12 in pants, you could try a one piece in a size 12H for the same cup volume.
Or if you wear a size 8F bra, but a size 14 pants, you could try a size 14D suit.
If your bra band size is larger than your regular dress size (for example, you wear a 16D and a size 12 in dresses) it's likely you're wearing the wrong bra size. Learn more here.
Sister sizing isn't always exact. There might be small cup size discrepancies across your sister row.