The Alpha Size Converter
One size in, six brand answers out, with a rule most converters skip: where a brand publishes its bra-to-alpha map, you get the exact letter; where it does not, you get the brand's actual system and what to check, instead of a guess dressed as an answer.
Convert it
The letter is not a standard
S, M and L are compressions, not conversions: each letter absorbs several band-and-cup combinations, and each brand chooses which ones. That is the entire argument of the alpha sizing page, and it is why this tool refuses to print one confident grid for every brand. At our checks of published guidance, Aerie's and Skims' medium covered essentially the same underbust range while fitting differently because the fabrics differ; Lively sells no standalone M at all. A converter that hides those facts behind one tidy table is lying by layout.
So the results above do three different, honest things. Where a brand publishes its map, the exact letter with the map cited. Where a brand's system is documented but per-product, the system plus exactly what to open on the product page. And where your size sits outside a brand's stretch range entirely, it says so and routes you to the size guides that list who does cut it.
Between letters, and past them
Straddling a line: the smaller letter works harder, the larger wears kinder. Compression sport and swim reward the smaller; lounge and long days reward the larger; and where a brand sells in-between jump sizes, as Skims documents, take the admission and the in-between size.
Past roughly DD: the honest flag the tool raises. The letter matching your ribcage stops matching your volume, no stretch fabric closes that gap with support intact, and the answer stops being alpha at all: bra-sized styles in your measured size, which the tool links directly.
Alpha conversion, answered
How do I convert my bra size to S, M, or L?
Start with the common convention, which this tool computes, then check the specific brand: each draws its own lines, and only some publish an exact bra-to-alpha map. Where a map exists, as at Pepper, the tool gives the exact letter; where it does not, the tool tells you what that brand's system is and what to check on the product page.
Why does the tool not give one exact letter for every brand?
Because the brands do not publish one, and inventing it would be guessing with confidence. Skims and Aerie run alpha on stretch styles with conversion details living on individual product pages; Lively sells combined sizes covering stated ranges. The honest conversion is the convention letter plus the brand's own rule.
What if I straddle two letters?
Normal, and the tool flags it. Tiebreak by the garment's job: the smaller letter works harder in compression and sport, the larger is kinder over long hours, and in swim or high-stretch fabric the smaller usually survives water and wear better.
Which brands run alpha sizing at all?
In our documented set: Aerie, Skims, Lively, Knix, Nike and Savage X Fenty on stretch styles, Pepper on its wirefree line with a published per-letter map, and Uniqlo and H&M on the high street. Structured styles at most of these still carry real band-and-cup sizes, which is why your measured size remains the anchor.
Opens HauteFlair’s own hub page; use your measured size there. 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.
Letters guess. Your size knows.
Every result above keys off your measured band and cup: two minutes to certainty.
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