Bra Size Guide — Fitting for Large Busts

Why Most Women Are in the Wrong Bra Size

Studies consistently suggest that the majority of women are wearing incorrectly sized bras — most commonly with a band too large and cup too small. This happens because mainstream bra fitting advice ("add 4 inches to your underbust measurement for band size") is based on outdated measurement methods. Modern fitting advice uses the underbust measurement directly for band size and a full bust measurement for cup calculation. The result is typically a smaller band and significantly larger cup than women are used to wearing.

How to Measure

Band size: Measure directly under the bust, pulled firm, in inches. Round to the nearest even number. This is your band size. Cup size: Measure at the fullest part of the bust, loosely. Subtract your band measurement from this number. Each inch of difference represents one cup size: 1"=A, 2"=B, 3"=C, 4"=D, 5"=DD/E, 6"=DDD/F, and so on. Example: 30" underbust, 38" bust = 8 inch difference = a UK G cup or US H cup (sizing systems differ).

Sister Sizes

If your calculated size isn't available, sister sizing allows you to move up a band size and down a cup, or down a band and up a cup, while keeping the same cup volume. Example: 32GG (UK) and 34G (UK) contain the same cup volume on different band widths. Sister sizing is useful when finding specific sizes in specific brands.

After Augmentation

Breast augmentation changes your bra size, often significantly. Post-surgery fitting should wait until swelling has fully resolved — typically 3–6 months post-operation. The new size may require brands or retailers specialising in large cup sizes (see our lingerie guide for recommendations). Very large implants (above approximately 1,000cc) may require custom bra solutions.