AB cup size is a combined measurement used in some international bra sizing systems to indicate a small bust. It represents a band size of 34 inches and a cup size smaller than A. The term originates from European and Japanese sizing conventions, where AA and A cups are often grouped under AB for simplicity.
Unlike standard US sizing, which uses separate numbers for band size and letters for cup volume, AB combines both. For example, a 34AB corresponds to a 34-inch underbust measurement with minimal projection, typically fitting busts 1-2 inches larger than the band.
The AB designation helps manufacturers standardize sizing across regions where cup increments differ. In the US, this would equate to an AA or A cup, depending on the brand. However, always measure carefully, as sizing varies by maker.
| Band Size | Bust Difference | US Equivalent |
|---|---|---|
| 32AB | 1 inch | 32AA |
| 34AB | 1-2 inches | 34AA/34A |
| 36AB | 1-2 inches | 36AA/36A |
AB sizing ensures better fit consistency for petite busts in regions where AA cups aren't standard. Many brands offering AB sizes also provide narrower wires and lighter padding to accommodate smaller frames. This reduces discomfort from ill-fitting bras, which can cause shoulder pain or poor posture.
For context, a 2018 study in the Journal of Physical Therapy Science found that 68% of women wearing incorrectly sized bras experienced back pain. Proper sizing, including AB cups when applicable, helps mitigate this risk.
Some assume AB is a single cup size, but it actually spans multiple band sizes. Others confuse it with US A cups, which may run larger. For example, a 34AB in European brands might fit like a 34A in US sizing, but not always.
To avoid confusion, measure your underbust and bust accurately. Subtract the underbust from the bust measurement to find your cup size. For instance, if your underbust is 34 inches and your bust is 36 inches, you'd likely wear a 34AB in Europe or a 34A in the US.
When shopping internationally, check the retailer's sizing guide. Some brands, like Triumph and Chantelle, offer AB sizes, while others may not. Always try bras on when possible, as fabric stretch and design affect fit.
I once helped a friend order bras from a Japanese online store. Her US 34A fit poorly, but switching to 34AB in the international size resolved the issue. The AB designation accounted for differences in cup depth and wire width, providing a snugger fit.
AB cups differ from AA and A primarily in regional availability. While AA cups exist in the US, they're rare in Europe and Asia, where AB serves the same purpose. Some brands use AB to simplify sizing charts, grouping very small cups together.
For larger cup sizes, the progression follows standard letter increments (B, C, D, etc.). However, AB remains unique to certain markets. If you're between sizes, consider whether your bra needs adjustability or specialized designs.