What a 40AA Actually Looks Like
A 40-inch band sits snugly around your ribcage just under your bust. Paired with an AA cup, that means roughly a 0-inch gap between your underbust and fullest-bust measurement. The band should feel snug on the loosest hook when new, since it will stretch slightly with wash and wear.
Sister Sizes for 40AA
If 40AA isn’t quite right, the two closest sister sizes are 42AA (looser band, bigger cup, same volume) and 38A (snugger band, smaller cup, same volume). Every 2-inch band change pairs with exactly one cup-letter change in the opposite direction, because both numbers describe the same underlying volume.
40AA in Other Sizing Systems
| System | Band | Cup |
|---|---|---|
| United States | 40″ | AA |
| United Kingdom | 40″ | AA |
| Europe (FR/ES/BE) | 120cm | AA |
| Italy | 120cm | AA |
| Japan/Korea | 100cm | AA |
Fit Tips at This Size
Raise both arms overhead; if the band rides up more than an inch, it’s too loose regardless of how it felt standing still. Cut varies more between brands at this size than the label suggests. Treat any brand’s chart as a starting point and expect to adjust half a size either way.
Want your exact size instead of an estimate? Use the Main Bra Calculator- free, private, takes under a minute.
Common Mistakes at 40AA
Buying based on the number alone without trying the style. Construction varies enough between brands that the same labeled size can fit two completely different ways.
Where to Actually Find This Size
Online shopping generally offers a wider real selection at this size than walking into a physical store, simply because warehouse inventory isn’t limited by shelf space the way retail floors are.
A Common Myth Worth Clearing Up
A common myth is that larger cup letters always mean an objectively “bigger” body overall. Cup size is about local volume relative to band size, not a measure of overall body size.
Style Recommendations for 40AA
Balconette and demi styles tend to work well here since they don’t rely on excess fabric to create shape.
Why This Number Isn’t Permanent
Weight fluctuation of even a few pounds can nudge a band size, especially at the boundary between two sizes. This isn’t a flaw in the measuring process, just how bodies naturally vary.
Shopping Online at This Size
Reading recent reviews that mention true-to-size feedback for the exact style (rather than the brand generally) is one of the more reliable ways to predict fit before buying online.