UK to US conversion

UK 40C in US Bra Size

Convert 40C from UK sizing to US sizing, with the full international table, sister sizes, and practical fit checks in one place.

Instant answer

40C (UK) =

40C US

In this sizing table, 40C in UK sizing converts to 40C in US sizing.

Full conversion table for 40C (US 40C)

40C bra size conversion across US, UK, EU, French, and Australian sizing.
US	UK	EU	FR	AU
40C	40C	90C	105C	18C

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

What this conversion means

The US equivalent for 40C is 40C 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 (40C)

Sister sizes: 38D can be worth checking when the cup volume feels close but the band needs a different feel.

What measurements make a 40C?

The useful way to read 40C is to separate the band from the cup step. In the current calculator formula, the closest starting range is about 39-41 inches (99-104 cm) under the bust and about 42.5-43.5 inches (108-110 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 40C as the US equivalent for those measurement notes.

Is 40C big or small?

Whether 40C feels small, average, or full depends on the body and on the brand. In this size set, the US equivalent uses a fuller 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 40C 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 40C differs between brands

40C 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 40C

40C 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.

Bras in your size

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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 40C the same as 40C in the US?

In this dataset, 40C (UK) converts to 40C 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 40C in European sizing?

40C (UK) matches the same base record as 90C (EU). The full table on this page shows each supported label side by side.

How do I check the fit of 40C?

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 40C?

38D are the closest sister-size options for 40C 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 40C?

40C maps to US 40C here. The current calculator formula points to about 39-41 inches underbust and 42.5-43.5 inches bust, or roughly 99-104 cm and 108-110 cm. Treat that as a starting range and then check the real fit.