30A vs 30B
One cup letter apart on the same band. Here is what one inch of difference actually changes, and how to know which is yours.
30A or 30B, in short
30A and 30B share the 30 band; 30B holds one cup step more volume: about one inch of bust. You are 30B if 30A spills, floats at the gore or puts the wire on tissue; you are 30A if 30B gapes or wrinkles at the top. If the band is wrong in either, that is a sister-size change, not a cup change.
30A and 30B, side by side
Same band bar, bigger dome: one inch more bust on the same frame: the cup grows, the band does not.
30A or 30B?
- 30A cups spill over the top or at the sides
- The gore floats off the sternum in a 30A
- The wire sits on breast tissue in a 30A
- 30B cups gape or wrinkle at the top
- 30B molded cups leave a hollow at the apex
- 30A fills evenly with a smooth top edge
Both share the 30 band. If the band is wrong in either, that is a separate fix: sister sizes (28B / —), not a cup change.
Brands that carry both 30A and 30B
Range-checked against each brand's core collections, with both sizes written in the brand's own notation.
| Brand | 30A as | 30B as | System | How it runs |
|---|---|---|---|---|
| Wacoal | 30A | 30B | US | Band true to size · cups true |
| Natori | 30A | 30B | US | Band soft / stretchy · cups grades small |
| Le Mystère | 30A | 30B | US | Band firm · cups true |
| Victoria's Secret | 30A | 30B | US | Band soft / stretchy · cups grades small |
| ThirdLove | 30A | 30B | US | Band true to size · cups grades generous |
| Savage X Fenty | 30A | 30B | US | Band soft / stretchy · cups true |
| Aerie | 30A | 30B | US | Band true to size · cups true |
| Cuup | 30A | 30B | US | Band true to size · cups true |
| Harper Wilde | 30A | 30B | US | Band true to size · cups true |
| Shock Absorber | 30A | 30B | UK | Band firm · cups true |
Every brand page converts your measured size and notes how it runs. All bra brands →
30A and 30B in every system
| US | UK | EU / DE / JP | FR / ES | AU / NZ | IT |
|---|---|---|---|---|---|
| 30A | 30A | 65A | 80A | 8A | 1A |
| 30B | 30B | 65B | 80B | 8B | 1B |
The one-cup step is one letter in every alphabet, but above D the letters diverge (US DDD = UK E = EU F).
The five fit checks, 30A vs 30B
| Check | What right looks like | What it tells you here |
|---|---|---|
| Band | Level, snug on the loosest hook, two fingers underneath, no ride-up | Identical band in both: if it fails, change the band with a sister size, not the cup |
| Cups | Filled to the top edge with no gap and no spill | 30B fills where 30A spills; 30A fills where 30B gapes |
| Gore | Flat against the sternum | A floating gore in 30A points to 30B |
| Straps | Light duty, no digging | Unrelated to the cup step; a strap problem is a band problem |
| Wire | On the ribcage, not on tissue | Wire on tissue in 30A points to 30B |
What goes wrong choosing between 30A and 30B
| Mistake | Why it fails |
|---|---|
| Going up a band instead of a cup when 30A spills | A bigger band with the same letter is a bigger cup AND a looser band; 30B keeps the band and adds only volume |
| Sizing down to 30A for a 'lifted' look | Spillage isn't lift; it is a cup too small |
| Judging by a molded cup only | Molded cups exaggerate both gap and spill; check a seamed cup before deciding |
Availability, shape and the +4 check
Related comparisons
30A vs 30B: answered
What is the difference between 30A and 30B?
One inch of bust on the same 30″ band: 30A is a 1″ difference, 30B a 2″ difference. 30B holds one cup step more volume; the band is identical.
Is 30A bigger than 30B?
30B is bigger by one cup step (about an inch of bust). Same band.
Can I wear 30B instead of 30A?
Only if the 30A cups are actually too small: spillage, floating gore or wire on tissue. Going up a cup for a band problem makes both worse.
What are 30A and 30B in UK and EU sizing?
30A: UK 30A, EU 65A, FR 80A. 30B: UK 30B, EU 65B, FR 80B.
Do 30A and 30B fit the same in every brand?
The relationship holds everywhere; the fit doesn't. Brands with soft bands push you toward the snugger sister, firm bands toward the looser; brands whose cups grade small push you up a cup. The brand table above shows how each runs.
Which is more common, 30A or 30B?
30A is less common in mainstream stores; 30B is less common in mainstream stores.
Should I own both 30A and 30B?
Usually one is right and the other is a mistake in the cup, but shape-dependent: a molded style may fit in one and a seamed style in the other.
How do I measure to tell 30A from 30B?
Underbust snug (28.5–30.4″ gives band 30), bust at the fullest point; the difference sets the cup. Then confirm on the body with the five fit checks.
HauteFlair labels cups in UK letters, so these links already convert your size by position (a US DDD lands on a UK E, a US G on a UK F). HauteFlair is owned by the same company as Brasize.ai; that relationship never changes the sizing math, charts, or fit advice on this page. How this site makes money.
Not sure which you are?
Two measurements settle it, then read the guide for your size.
Calculate My Bra Size →