AU to US conversion

AU 12B in US Bra Size

Convert 12B from Australian sizing to US sizing, with the full international table, sister sizes, and practical fit checks in one place.

Instant answer

12B (AU) =

34B US

In this sizing table, 12B in Australian sizing converts to 34B in US sizing.

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If you are starting from body measurements instead of a known label, use the AU/NZ calculator with centimetres selected by default.

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Full conversion table for 12B (US 34B)

34B bra size conversion across US, UK, EU, French, and Australian sizing.
US	UK	EU	FR	AU
34B	34B	75B	90B	12B

Bra sizing varies between brands. Use this as an accurate starting point and check the fit.

What this conversion means

Australian sizing can look unfamiliar because the band and cup sequences are not always written like US labels. For 12B, this shared data file maps the fit target to 34B in US sizing.

Sister sizes for the US equivalent (34B)

Sister sizes: 32C and 36A can be worth checking when the cup volume feels close but the band needs a different feel.

What measurements make a 12B?

12B starts with the underbust, then adds cup depth from the bust measurement. In the current calculator formula, the closest starting range is about 33-35 inches (84-89 cm) under the bust and about 35.5-36.5 inches (90-93 cm) around the fullest part of the bust. The band comes from the underbust rounding, while the cup step comes from the difference between bust and band. This page uses 34B as the US equivalent for those measurement notes.

Is 12B big or small?

The label 12B can look more dramatic than it fits, especially across systems. In this size set, the US equivalent uses a middle band and a lower cup step. Cup letters are relative to the band, so a D on one band is not the same volume as a D on every other band. The most useful question is whether the band stays level and the cups hold smoothly, not whether the label sounds large or small.

If 12B doesn't fit right

Band rides up: The band may be too loose or stretched out; try a snugger band or compare the snugger sister size.

Cups gape: The cup may be too roomy, too deep, or pulled away by a loose band; check the band before changing cup volume.

Cups spill: The cup volume may be too small or the cup shape may be too closed; try one cup step up before changing the band.

Straps dig in: The straps may be compensating for a band that is not supporting enough; reset the band fit before tightening straps.

How 12B differs between brands

Brand sizing matters for 12B because cup depth, wire width, and band stretch are design choices. A firmer elastic can make the same band feel smaller, and a shallow or narrow cup can make the same cup letter feel different. Check the retailer chart, read fit notes when available, and compare the label against the brand and region sizing guide before treating the conversion as final.

Shopping for 12B

A good shopping path for 12B starts with everyday support, then moves into outfit-specific shapes. If the cup is in a lower or middle step, lightly lined T-shirt styles can make gaps easy to spot. Fuller cup steps often benefit from styles with steadier side support, deeper cups, or a balconette shape depending on breast shape. For special outfits, compare the fit needs in the outfit guides before choosing a strapless, plunge, or backless option.

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Everyday Fit Store

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Comfort Band Co.

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Soft Cup Edit

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FAQ

Is 12B the same as 34B in the US?

In this dataset, 12B (AU) converts to 34B in US sizing. Some brands publish their own charts, so use this as the closest standard label and still check the real fit.

What is 12B in French sizing?

12B (AU) matches the same base record as 90B (FR). The full table on this page shows each supported label side by side.

How do I check the fit of 34B?

A good US fit should feel secure without digging. If 34B feels close in the cup but wrong in the band, compare the sister sizes before changing cup volume.

What sister sizes work with 34B?

32C and 36A are the closest sister-size options for 34B in this dataset. Try a sister size when cup volume feels close but the band needs to feel snugger or looser.

Why do bra sizes differ between countries?

Bra labels are written differently across US, UK, EU, French, and Australian systems. Cup letters can also diverge after D, so a converted label is a starting point rather than a promise of identical fit.

What measurements usually make 12B?

12B maps to US 34B here. The current calculator formula points to about 33-35 inches underbust and 35.5-36.5 inches bust, or roughly 84-89 cm and 90-93 cm. Treat that as a starting range and then check the real fit.