FCFitCircle
Bra sister size chart

Keep the cup volume close while you move the band where it actually feels wearable.

Start from the size that almost works, then use sister sizes to test the next sensible band swap instead of bouncing through random sizes.

Size converter

Looser band36C
Current34D
Tighter band32DD

Try 36C first when the cups feel right but the band feels too firm.

Tight band, right cup

Go one band up and one cup down when the cups feel right but the band feels too firm.

Loose band, slipping straps

Go one band down and one cup up when the straps overwork because the band is not anchoring well.

Stay close to the starting size

One or two steps away is usually enough. Past that point, shape and wire width start changing too much.

Quick sister size chart examples

Starting sizeNearby swapsWhen it helps
32D30DD / 34CBand changed, cup volume stayed close.
34DD32E / 36DUseful when the wire is right but the band feels off.
36G34GG / 38FFHelpful for fuller cups where stock runs uneven by brand.
38B36C / 40ACommon when a bralette or soft cup runs looser in the band.