38A vs 38B
One cup letter apart on the same band. Here is what one inch of difference actually changes, and how to know which is yours.
38A or 38B, in short
38A and 38B share the 38 band; 38B holds one cup step more volume: about one inch of bust. You are 38B if 38A spills, floats at the gore or puts the wire on tissue; you are 38A if 38B gapes or wrinkles at the top. If the band is wrong in either, that is a sister-size change, not a cup change.
38A and 38B, side by side
Same band bar, bigger dome: one inch more bust on the same frame: the cup grows, the band does not.
38A or 38B?
- 38A cups spill over the top or at the sides
- The gore floats off the sternum in a 38A
- The wire sits on breast tissue in a 38A
- 38B cups gape or wrinkle at the top
- 38B molded cups leave a hollow at the apex
- 38A fills evenly with a smooth top edge
Both share the 38 band. If the band is wrong in either, that is a separate fix: sister sizes (36B / —), not a cup change.
Brands that carry both 38A and 38B
Range-checked against each brand's core collections, with both sizes written in the brand's own notation.
| Brand | 38A as | 38B as | System | How it runs |
|---|---|---|---|---|
| Wacoal | 38A | 38B | US | Band true to size · cups true |
| Natori | 38A | 38B | US | Band soft / stretchy · cups grades small |
| Le Mystère | 38A | 38B | US | Band firm · cups true |
| Victoria's Secret | 38A | 38B | US | Band soft / stretchy · cups grades small |
| Maidenform | 38A | 38B | US | Band true to size · cups true |
| Soma | 38A | 38B | US | Band true to size · cups true |
| ThirdLove | 38A | 38B | US | Band true to size · cups grades generous |
| Savage X Fenty | 38A | 38B | US | Band soft / stretchy · cups true |
| Aerie | 38A | 38B | US | Band true to size · cups true |
| Cuup | 38A | 38B | US | Band true to size · cups true |
Every brand page converts your measured size and notes how it runs. All bra brands →
38A and 38B in every system
| US | UK | EU / DE / JP | FR / ES | AU / NZ | IT |
|---|---|---|---|---|---|
| 38A | 38A | 85A | 100A | 16A | 5A |
| 38B | 38B | 85B | 100B | 16B | 5B |
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, 38A vs 38B
| 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 | 38B fills where 38A spills; 38A fills where 38B gapes |
| Gore | Flat against the sternum | A floating gore in 38A points to 38B |
| 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 38A points to 38B |
What goes wrong choosing between 38A and 38B
| Mistake | Why it fails |
|---|---|
| Going up a band instead of a cup when 38A spills | A bigger band with the same letter is a bigger cup AND a looser band; 38B keeps the band and adds only volume |
| Sizing down to 38A 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
38A vs 38B: answered
What is the difference between 38A and 38B?
One inch of bust on the same 38″ band: 38A is a 1″ difference, 38B a 2″ difference. 38B holds one cup step more volume; the band is identical.
Is 38A bigger than 38B?
38B is bigger by one cup step (about an inch of bust). Same band.
Can I wear 38B instead of 38A?
Only if the 38A 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 38A and 38B in UK and EU sizing?
38A: UK 38A, EU 85A, FR 100A. 38B: UK 38B, EU 85B, FR 100B.
Do 38A and 38B 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, 38A or 38B?
38A is less common in mainstream stores; 38B is one of the most widely stocked sizes.
Should I own both 38A and 38B?
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 38A from 38B?
Underbust snug (36.5–38.4″ gives band 38), 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.
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