AU to US conversion

AU 12C in US Bra Size

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

Instant answer

12C (AU) =

34C US

In this sizing table, 12C in Australian sizing converts to 34C 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 12C (US 34C)

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

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

What this conversion means

The US equivalent for 12C is 34C here. If the converted cup volume feels close but the band feels too snug or loose, use the sister sizes below before jumping several cup letters.

Sister sizes for the US equivalent (34C)

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

What measurements make a 12C?

The useful way to read 12C is to separate the band from the cup step. In the current calculator formula, the closest starting range is about 33-35 inches (84-89 cm) under the bust and about 36.5-37.5 inches (93-95 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 34C as the US equivalent for those measurement notes.

Is 12C big or small?

Whether 12C feels small, average, or full depends on the body and on the brand. In this size set, the US equivalent uses a middle band and a middle 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 12C 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 12C differs between brands

12C can shift in feel from one retailer to another because brands grade bands and cups in their own way. 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 12C

12C is easiest to compare when you try shapes that show both cup volume and band tension clearly. 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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FAQ

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

In this dataset, 12C (AU) converts to 34C 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 12C in UK sizing?

12C (AU) matches the same base record as 34C (UK). The full table on this page shows each supported label side by side.

How do I check the fit of 34C?

Check that the band stays level, the cups sit smoothly without spilling or gapping, and the straps are not doing all the support work. The converted US size is a starting point, not a guarantee.

What sister sizes work with 34C?

32D and 36B are the closest sister-size options for 34C 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 12C?

12C maps to US 34C here. The current calculator formula points to about 33-35 inches underbust and 36.5-37.5 inches bust, or roughly 84-89 cm and 93-95 cm. Treat that as a starting range and then check the real fit.