US to UK conversion

40C in UK Bra Size

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

Instant answer

40C (US) =

40C UK

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

Sizing varies by brand

A conversion gives you the closest label in another sizing system, but brands can grade cups, wires, and bands differently. Use the converted size as a starting point, then check the retailer's chart and the fit of the actual bra.

Before you buy in UK sizing

Use 40C as the translated label, not as a fit guarantee.
Check the retailer's size chart because some brands grade bands and cups differently.
If the cup volume feels close but the band changes, compare sister sizes before switching cup letters.
When possible, check return rules before buying across sizing systems.

Full conversion table for 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.

Sizes near 40C in UK sizing

If 40C is close but not right, these are the neighbouring US sizes and what each one becomes in UK sizing. Band neighbours change the fit around the ribcage; cup neighbours change volume.

US sizes adjacent to 40C and their UK equivalents.
US size	UK size	How it differs
38C	38C	One band step snugger, same cup letter.
40B	40B	One cup step down, same band.
40D	40D	One cup step up, same band.

What this conversion means

The 40 band is the base of 40C, and the C cup is converted through the UK cup sequence where needed. That gives 40C in UK sizing. Use the sister sizes below if the cup volume seems close but the band does not feel right.

Sister sizes for 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.

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

Placeholder for a broad size range and return-friendly basics.

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Comfort Band Co.

Placeholder for supportive everyday styles by band and cup.

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Soft Cup Edit

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FAQ

Is 40C in the US the same as UK sizing?

Not exactly. 40C is the US label, and this table converts it to 40C in UK sizing, though some brands publish their own charts.

What is 40C in European sizing?

In this same table, 40C converts to 90C (EU). That helps when a retailer shows a European chart instead of a UK one.

How do I know if 40C fits?

Check that the band stays level, the cups do not spill or gap, and the center gore sits close if the bra has wires. If the cup feels right but the band feels wrong, try a sister size.

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?

Countries and brands do not all use the same band labels or cup-letter sequence. A conversion translates the closest standard label, but the final fit still depends on the specific bra.

What measurements usually make 40C?

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.