28AA Bra Size Guide: Measurements, Fit, Sister Sizes & Conversions

Last updated: August 2026

The 28AA bra size pairs a 28 band with an AA cup. This guide breaks down exactly what that means in real measurements, how to tell whether 28AA is truly your size, which sister sizes to reach for, and how 28AA converts around the world.

Band 28AA cupUnderbust 27–28″Bust 28–29″

What a 28AA bra actually means

Read a bra size as two parts. The 28 is the band, and it comes straight from your underbust — the snug measurement around your ribcage just beneath the bust. The AA is the cup, and it comes from how much bigger your bust is than that underbust: about 0–1 inches more for an AA cup. The cup letter is a difference, not a fixed volume — which is why the very same cup looks different on a narrow band than on a wide one.

28AA measurements

If your own numbers land inside those ranges, 28AA is your calculated size. If you are close but not quite, the sister sizes below will usually have you covered.

How to measure yourself for a 28AA

You need a soft tape measure and, ideally, a non-padded bra. Stand up straight and breathe normally — measuring too tight is the most common reason people end up in the wrong size.

• Underbust: wrap the tape snugly around your ribcage directly under the bust, level all the way round. For a 28 band you are looking for roughly 27–28 inches (69–71 cm).
• Bust: measure loosely around the fullest part, tape parallel to the floor. For 28AA that is about 28–29 inches (71–74 cm).
• Subtract: bust minus underbust gives you the cup. A gap of about 0–1 inches is the AA cup that makes 28AA.

How to check the fit is actually right

Numbers get you to the right size on paper; these hands-on checks tell you whether it fits in real life. Do them in front of a mirror, wearing the bra on the loosest hook:

• Band: it should sit level all the way around, in line with the front. Slide two fingers under it at the back — snug, not loose, no riding up when you raise your arms. The band does roughly 80% of the support work, so this matters most.
• Cups: do a quick “scoop and swoop” — lean forward, settle everything into the cup, then stand up. There should be no spillage over the top or sides, and no wrinkling or gaping at the edge. Spillage means size up a cup; gaping means size down a cup.
• Centre gore: the little bridge between the cups should lie flat against your breastbone. If it floats off the body, the cup is usually too small.
• Straps: you should fit a finger under them comfortably. If they dig in or carry most of the weight, the band is too loose — tighten it or size the band down.

28AA in international sizing

So a US 28AA is written 28AA in the UK, 60AA across much of the EU and 75AA in France. The band number and the cup letter can both change between systems, which is why the same bra can look like two different sizes depending on where it was made.

Sister sizes of 28AA

Sister sizes hold the same cup volume as 28AA but on a different band — the natural sizes to try when the band feels tight or loose. Here is the 28AA sister family:

Common fit problems with a 28AA — and how to fix them

• Cups wrinkling or gaping: a 28AA is a shallow cup, so a stiff or moulded cup can pucker. Unlined, stretch or triangle styles usually sit smoother.
• Band riding up at the back: 28 is a narrow band and can creep up if it is even slightly loose. It should sit level with the front; if it rides up, go down a band and up a cup (a sister size).

Best bra styles for a 28AA

For a 28AA, look to bralettes, triangle bras, plunge and lightly-padded push-up styles, which add shape without gaping. On a narrow band, seek-out brands that cut small bands generously so the wing still feels supportive. Whatever the style, get the band right first — it is the foundation every other part of the fit sits on.

Where to find 28AA bras

28AA falls outside the core high-street band, so everyday shops may carry fewer options. Specialist fuller-bust or extended-size retailers will have far more choice, and knowing your sister sizes widens what you can wear when a specific size is out of stock.

Is 28AA big or small?

28AA sits in the shallow range for cups on a smaller band. Whether that reads as ‘big’ or ‘small’ depends entirely on the band it sits on: the cup volume of 28AA is identical to every sister size in the table above, even though the letters differ. That is the single most useful thing to understand about bra sizing — the letter alone tells you very little without the band.

Related sizes and comparisons

• 28AA vs 28A — one cup larger on the same band.
• 26A guide — a sister size of 28AA.
• 30AA guide — a sister size of 28AA.