G Cup Sister Size Calculator and Chart

Use it when the cups seem right but the band alone feels too loose or too tight. One smaller band takes one higher cup step; one larger band takes one lower cup step.

If the band is comfortable and level but the cups spill, compare more cup capacity on that same band. If the cups gap while pressure remains elsewhere, investigate cup shape. A sister size is not the default solution to every fit problem.

Several sister-size moves can dramatically alter strap position, wire shape and band support. A technically similar nominal cup capacity does not make every distant sister size wearable. Prefer an adjacent comparison and assess the whole garment.

Consider UK 34G with cups that contain the tissue well and a band that rides up. The adjacent 32GG comparison reduces the band while retaining similar nominal cup capacity. Choosing 32G instead would reduce the cup capacity as well, changing two fit dimensions at once.

If the 34 band feels too tight when tested independently, 36FF is the adjacent UK comparison. But if it only feels tight when the cups are worn normally, first consider inadequate cup depth or capacity. Increasing the band can disguise the original problem.

A larger frame can move straps farther apart or change how wires surround tissue. Two garments with similar nominal capacity may distribute that space differently. Judge containment and comfort after moving, not only while standing in front of a mirror.

Use the diagram to follow the label arithmetic. Its identical bra icons intentionally do not promise identical dimensions or silhouettes. A label relationship is a starting comparison, not a physical specification.

For UK 34G, moving to band 32 requires the next cup step, GG, to retain similar nominal capacity. Moving to band 36 requires the previous step, FF. The complete adjacent comparisons are therefore 32GG and 36FF. In the US ladder, 34G instead leads to 32H and 36DDD. Treating letters as ordinary alphabet positions would miss the double-letter steps.

Choose the direction based on a band observation. If the band is stable and comfortable but the cup spills, do not use a sister-size move as a substitute for adding cup capacity. If the band alone is too loose while cups contain well, an adjacent smaller-band comparison can isolate the question more effectively.

Moving several bands away can alter the frame substantially. Strap placement, wire shape and cup height need not remain suitable merely because a nominal capacity relationship can be calculated. The tool deliberately emphasises adjacent sizes so the output stays close to a realistic comparison task.

When a shop lacks your size, record the original full label and investigate another model or range before treating a distant substitute as equivalent. If you do try an adjacent size, repeat the band, edge and movement checks. The arithmetic preserves a grading relationship, not a promise that both bras will feel alike.