Bra sizes that share the same color  "sister size" - an equivalent size that holds the same volume as your cup (even if it is a different letter). Need to go down a band size? Follow the same color in the chart to the lower band size and you'll see what cup you need.  If you wish to go up a band you need to go down a cup. The band size increases as you move from top to bottom. The cup size increases as you move from left to right on the chart.