US to FR conversion

40B in French Bra Size

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

Instant answer

40B (US) =

105B FR

In this sizing table, 40B in US sizing converts to 105B in French 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 French sizing

Use 105B 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 40B

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

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

Sizes near 40B in French sizing

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

US sizes adjacent to 40B and their French equivalents.
US size	FR size	How it differs
38B	100B	One band step snugger, same cup letter.
40A	105A	One cup step down, same band.
40C	105C	One cup step up, same band.

What this conversion means

If you searched for 40b french size, the short answer is 105B. The full table shows the same US size across every supported system so you can compare retailer charts without opening several pages.

Sister sizes for 40B

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

What measurements make a 40B?

40B is built from a band measurement and a bust measurement, not from the label alone. In the current calculator formula, the closest starting range is about 39-41 inches (99-104 cm) under the bust and about 41.5-42.5 inches (105-108 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 40B big or small?

40B is not automatically big or small; it depends on the band and the cup together. In this size set, the US equivalent uses a fuller 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 40B 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 40B differs between brands

Two brands can print 40B or its equivalent on the tag and still cut the bra differently. 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 40B

When shopping for 40B, start with styles that make the band easy to judge. 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

Looking for 40B? We may earn a commission if you buy through sponsored links.

Everyday Fit Store

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

→

Comfort Band Co.

Placeholder for supportive everyday styles by band and cup.

→

Soft Cup Edit

Placeholder for wire-free and lounge options.

→

FAQ

Is 40B in the US the same as French sizing?

Use 105B as the French match for 40B in this dataset. The label may look similar in some systems, but it still belongs to a different sizing sequence.

What is 40B in Australian sizing?

In this same table, 40B converts to 18B (AU). That helps when a retailer shows a Australian chart instead of a French one.

How do I know if 40B fits?

A good fit should feel secure without digging. Watch for a band that rides up, cups that wrinkle, or straps carrying most of the support.

What sister sizes work with 40B?

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

The current calculator formula points to about 39-41 inches underbust and 41.5-42.5 inches bust, or roughly 99-104 cm and 105-108 cm. Treat that as a starting range and then check the real fit.